diff --git a/crates/fbuild-build/src/apollo3/orchestrator.rs b/crates/fbuild-build/src/apollo3/orchestrator.rs
index 2cdddb90..7836ba23 100644
--- a/crates/fbuild-build/src/apollo3/orchestrator.rs
+++ b/crates/fbuild-build/src/apollo3/orchestrator.rs
@@ -55,7 +55,21 @@ impl BuildOrchestrator for Apollo3Orchestrator {
         .await;
 
         // 4. Ensure Apollo3 cores (SparkFun Arduino Apollo3 core)
-        let framework = fbuild_packages::library::Apollo3Cores::new(&params.project_dir);
+        // Honor `platform_packages` override from the env section
+        // (FastLED/fbuild#664, #681): if set, the override URL replaces the
+        // const-pinned default and gets its own cache subdir via
+        // `PackageBase::with_override`.
+        let __ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduinoambiqapollo3")
+            });
+        let framework = match __ovr {
+            Some(o) => fbuild_packages::library::Apollo3Cores::with_override(&params.project_dir, o),
+            None => fbuild_packages::library::Apollo3Cores::new(&params.project_dir),
+        };
         let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
         tracing::info!("Apollo3 cores at {}", framework_dir.display());
 
diff --git a/crates/fbuild-build/src/ch32v/orchestrator.rs b/crates/fbuild-build/src/ch32v/orchestrator.rs
index 0b159424..b33b0f39 100644
--- a/crates/fbuild-build/src/ch32v/orchestrator.rs
+++ b/crates/fbuild-build/src/ch32v/orchestrator.rs
@@ -53,7 +53,18 @@ impl BuildOrchestrator for Ch32vOrchestrator {
         .await;
 
         // 4. Ensure OpenWCH CH32V cores
-        let framework = fbuild_packages::library::Ch32vCores::new(&params.project_dir);
+        // Honor `platform_packages` override (FastLED/fbuild#664, #681).
+        let __ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduino-ch32v")
+            });
+        let framework = match __ovr {
+            Some(o) => fbuild_packages::library::Ch32vCores::with_override(&params.project_dir, o),
+            None => fbuild_packages::library::Ch32vCores::new(&params.project_dir),
+        };
         let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
         tracing::info!("CH32V cores at {}", framework_dir.display());
 
diff --git a/crates/fbuild-build/src/esp8266/orchestrator.rs b/crates/fbuild-build/src/esp8266/orchestrator.rs
index 719f9b57..686dbcaf 100644
--- a/crates/fbuild-build/src/esp8266/orchestrator.rs
+++ b/crates/fbuild-build/src/esp8266/orchestrator.rs
@@ -59,7 +59,20 @@ impl BuildOrchestrator for Esp8266Orchestrator {
         .await;
 
         // 4. Ensure framework
-        let framework = fbuild_packages::library::Esp8266Framework::new(&params.project_dir);
+        // Honor `platform_packages` override (FastLED/fbuild#664, #681).
+        let __ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduinoespressif8266")
+            });
+        let framework = match __ovr {
+            Some(o) => {
+                fbuild_packages::library::Esp8266Framework::with_override(&params.project_dir, o)
+            }
+            None => fbuild_packages::library::Esp8266Framework::new(&params.project_dir),
+        };
         let _framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
         tracing::info!("ESP8266 framework ready");
         let board_id = ctx
diff --git a/crates/fbuild-build/src/nrf52/orchestrator.rs b/crates/fbuild-build/src/nrf52/orchestrator.rs
index de100ca8..ebe31945 100644
--- a/crates/fbuild-build/src/nrf52/orchestrator.rs
+++ b/crates/fbuild-build/src/nrf52/orchestrator.rs
@@ -84,7 +84,18 @@ impl BuildOrchestrator for Nrf52Orchestrator {
         .await;
 
         // 4. Ensure NRF52 cores (Adafruit nRF52 Arduino core)
-        let framework = fbuild_packages::library::Nrf52Cores::new(&params.project_dir);
+        // Honor `platform_packages` override (FastLED/fbuild#664, #681).
+        let __ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduinoadafruitnrf52")
+            });
+        let framework = match __ovr {
+            Some(o) => fbuild_packages::library::Nrf52Cores::with_override(&params.project_dir, o),
+            None => fbuild_packages::library::Nrf52Cores::new(&params.project_dir),
+        };
         let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
         tracing::info!("NRF52 cores at {}", framework_dir.display());
 
diff --git a/crates/fbuild-build/src/renesas/orchestrator.rs b/crates/fbuild-build/src/renesas/orchestrator.rs
index a5243ff1..30222b68 100644
--- a/crates/fbuild-build/src/renesas/orchestrator.rs
+++ b/crates/fbuild-build/src/renesas/orchestrator.rs
@@ -85,7 +85,20 @@ impl BuildOrchestrator for RenesasOrchestrator {
         .await;
 
         // 4. Ensure Renesas cores (ArduinoCore-renesas)
-        let framework = fbuild_packages::library::RenesasCores::new(&params.project_dir);
+        // Honor `platform_packages` override (FastLED/fbuild#664, #681).
+        let __ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduinorenesas")
+            });
+        let framework = match __ovr {
+            Some(o) => {
+                fbuild_packages::library::RenesasCores::with_override(&params.project_dir, o)
+            }
+            None => fbuild_packages::library::RenesasCores::new(&params.project_dir),
+        };
         let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
         tracing::info!("Renesas cores at {}", framework_dir.display());
 
diff --git a/crates/fbuild-build/src/rp2040/orchestrator.rs b/crates/fbuild-build/src/rp2040/orchestrator.rs
index e91b035c..27890a41 100644
--- a/crates/fbuild-build/src/rp2040/orchestrator.rs
+++ b/crates/fbuild-build/src/rp2040/orchestrator.rs
@@ -89,7 +89,18 @@ impl BuildOrchestrator for Rp2040Orchestrator {
         .await;
 
         // 4. Ensure RP2040 cores (arduino-pico by earlephilhower)
-        let framework = fbuild_packages::library::Rp2040Cores::new(&params.project_dir);
+        // Honor `platform_packages` override (FastLED/fbuild#664, #681).
+        let __ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduinopico")
+            });
+        let framework = match __ovr {
+            Some(o) => fbuild_packages::library::Rp2040Cores::with_override(&params.project_dir, o),
+            None => fbuild_packages::library::Rp2040Cores::new(&params.project_dir),
+        };
         let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
         tracing::info!("RP2040 cores at {}", framework_dir.display());
         let board_id = ctx
diff --git a/crates/fbuild-build/src/sam/orchestrator.rs b/crates/fbuild-build/src/sam/orchestrator.rs
index 45b4046a..959595fa 100644
--- a/crates/fbuild-build/src/sam/orchestrator.rs
+++ b/crates/fbuild-build/src/sam/orchestrator.rs
@@ -95,11 +95,21 @@ impl BuildOrchestrator for SamOrchestrator {
         .await;
 
         // 4. Ensure correct Arduino core based on MCU family
+        // Honor `platform_packages` override (FastLED/fbuild#664, #681). Only
+        // SAM (Due) is wired through this PR — SAMD's framework_name needs
+        // separate verification (see issue thread).
+        let __sam_ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduino-sam")
+            });
         let (framework_dir, core_dir, variant_dir, linker_script_path, system_includes) =
             if is_samd_mcu(&ctx.board.mcu) {
                 install_samd_core(params, &ctx.board.core, &ctx.board.variant).await?
             } else {
-                install_sam_core(params, &ctx.board.core, &ctx.board.variant).await?
+                install_sam_core(params, &ctx.board.core, &ctx.board.variant, __sam_ovr).await?
             };
 
         let build_dir = &ctx.build_dir;
@@ -308,8 +318,12 @@ async fn install_sam_core(
     params: &BuildParams,
     core_name: &str,
     variant_name: &str,
+    ovr: Option<fbuild_config::PackageOverride>,
 ) -> Result<(PathBuf, PathBuf, PathBuf, PathBuf, Vec<PathBuf>)> {
-    let framework = fbuild_packages::library::SamCores::new(&params.project_dir);
+    let framework = match ovr {
+        Some(o) => fbuild_packages::library::SamCores::with_override(&params.project_dir, o),
+        None => fbuild_packages::library::SamCores::new(&params.project_dir),
+    };
     let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
     tracing::info!("SAM cores at {}", framework_dir.display());
 
diff --git a/crates/fbuild-build/src/silabs/orchestrator.rs b/crates/fbuild-build/src/silabs/orchestrator.rs
index d314c346..380ae841 100644
--- a/crates/fbuild-build/src/silabs/orchestrator.rs
+++ b/crates/fbuild-build/src/silabs/orchestrator.rs
@@ -37,7 +37,18 @@ impl BuildOrchestrator for SilabsOrchestrator {
         )
         .await;
 
-        let framework = fbuild_packages::library::SilabsCores::new(&params.project_dir);
+        // Honor `platform_packages` override (FastLED/fbuild#664, #681).
+        let __ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduinosilabs")
+            });
+        let framework = match __ovr {
+            Some(o) => fbuild_packages::library::SilabsCores::with_override(&params.project_dir, o),
+            None => fbuild_packages::library::SilabsCores::new(&params.project_dir),
+        };
         let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
         tracing::info!("Silicon Labs cores at {}", framework_dir.display());
 
diff --git a/crates/fbuild-build/src/stm32/orchestrator/arduino_mbed.rs b/crates/fbuild-build/src/stm32/orchestrator/arduino_mbed.rs
index c224622c..d452cafe 100644
--- a/crates/fbuild-build/src/stm32/orchestrator/arduino_mbed.rs
+++ b/crates/fbuild-build/src/stm32/orchestrator/arduino_mbed.rs
@@ -38,7 +38,17 @@ pub(super) async fn build_arduino_mbed_stm32(
     let eh_frame_policy =
         crate::eh_frame_policy_compute::compute_eh_frame_policy(&ctx, params.profile, None);
 
-    let framework = fbuild_packages::library::ArduinoMbedCore::new(&params.project_dir);
+    // Honor `platform_packages` override from the env section
+    // (FastLED/fbuild#664, #681).
+    let __ovr = ctx
+        .config
+        .get_env_config(&params.env_name)
+        .ok()
+        .and_then(|env| crate::package_override::resolve_override(env, "framework-arduino-mbed"));
+    let framework = match __ovr {
+        Some(o) => fbuild_packages::library::ArduinoMbedCore::with_override(&params.project_dir, o),
+        None => fbuild_packages::library::ArduinoMbedCore::new(&params.project_dir),
+    };
     let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
     tracing::info!("Arduino mbed core at {}", framework_dir.display());
 
diff --git a/crates/fbuild-build/src/stm32/orchestrator/mod.rs b/crates/fbuild-build/src/stm32/orchestrator/mod.rs
index 7b43f8bd..00e4dd6c 100644
--- a/crates/fbuild-build/src/stm32/orchestrator/mod.rs
+++ b/crates/fbuild-build/src/stm32/orchestrator/mod.rs
@@ -81,7 +81,18 @@ impl BuildOrchestrator for Stm32Orchestrator {
         }
 
         // 4. Ensure STM32duino cores
-        let framework = fbuild_packages::library::Stm32Cores::new(&params.project_dir);
+        // Honor `platform_packages` override (FastLED/fbuild#664, #681).
+        let __ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduinoststm32")
+            });
+        let framework = match __ovr {
+            Some(o) => fbuild_packages::library::Stm32Cores::with_override(&params.project_dir, o),
+            None => fbuild_packages::library::Stm32Cores::new(&params.project_dir),
+        };
         let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
         tracing::info!("STM32 cores at {}", framework_dir.display());
 
diff --git a/crates/fbuild-build/src/teensy/orchestrator.rs b/crates/fbuild-build/src/teensy/orchestrator.rs
index e55345d1..88309067 100644
--- a/crates/fbuild-build/src/teensy/orchestrator.rs
+++ b/crates/fbuild-build/src/teensy/orchestrator.rs
@@ -100,7 +100,18 @@ impl BuildOrchestrator for TeensyOrchestrator {
         .await;
 
         // 4. Ensure Teensy cores
-        let framework = fbuild_packages::library::TeensyCores::new(&params.project_dir);
+        // Honor `platform_packages` override (FastLED/fbuild#664, #681).
+        let __ovr = ctx
+            .config
+            .get_env_config(&params.env_name)
+            .ok()
+            .and_then(|env| {
+                crate::package_override::resolve_override(env, "framework-arduinoteensy")
+            });
+        let framework = match __ovr {
+            Some(o) => fbuild_packages::library::TeensyCores::with_override(&params.project_dir, o),
+            None => fbuild_packages::library::TeensyCores::new(&params.project_dir),
+        };
         let framework_dir = fbuild_packages::Package::ensure_installed(&framework).await?;
         tracing::info!("Teensy cores at {}", framework_dir.display());
 
diff --git a/crates/fbuild-cli/tests/ci_command.rs b/crates/fbuild-cli/tests/ci_command.rs
index 74549712..e7ac200b 100644
--- a/crates/fbuild-cli/tests/ci_command.rs
+++ b/crates/fbuild-cli/tests/ci_command.rs
@@ -5,7 +5,7 @@
 //! produces usage errors. The inline parse tests in `main.rs::ci_tests`
 //! cover positive-parse + mutual-exclusion contracts at unit-test speed.
 
-use std::process::{Command, Output};
+use std::process::{Command, Output, Stdio};
 use std::time::{Duration, Instant};
 
 /// Run a `Command` with a hard wall-clock budget (FastLED/fbuild#806).
@@ -14,8 +14,14 @@ use std::time::{Duration, Instant};
 /// (e.g. a regression in clap parsing → infinite loop). 10 s is overkill
 /// for `--help` / argument-validation paths, but keeps the test runner
 /// from sitting on its 6 h job budget if the CLI ever does wedge.
+///
+/// stdout/stderr must be piped explicitly: `spawn()` inherits the parent
+/// streams by default, so without this `wait_with_output()` reports an
+/// empty stdout and the `--help`-content assertions panic spuriously.
+/// `Command::output()` pipes for you; `spawn()` does not.
 fn run_cli_or_timeout(mut cmd: Command) -> Output {
     let budget = Duration::from_secs(10);
+    cmd.stdout(Stdio::piped()).stderr(Stdio::piped());
     let mut child = cmd.spawn().expect("spawn fbuild");
     let deadline = Instant::now() + budget;
     loop {
diff --git a/crates/fbuild-cli/tests/lib_select.rs b/crates/fbuild-cli/tests/lib_select.rs
index ef77bc08..87aebb37 100644
--- a/crates/fbuild-cli/tests/lib_select.rs
+++ b/crates/fbuild-cli/tests/lib_select.rs
@@ -6,7 +6,7 @@
 //! that need a real framework install (Teensy, STM32, ...) are gated
 //! behind `#[ignore]` and run manually.
 
-use std::process::{Command, Output};
+use std::process::{Command, Output, Stdio};
 use std::time::{Duration, Instant};
 
 /// Run a `Command` with a hard wall-clock budget (FastLED/fbuild#806).
@@ -15,8 +15,14 @@ use std::time::{Duration, Instant};
 /// (e.g. a regression in clap parsing → infinite loop). 10 s is overkill
 /// for `--help` / argument-validation paths, but keeps the test runner
 /// from sitting on its 6 h job budget if the CLI ever does wedge.
+///
+/// stdout/stderr must be piped explicitly: `spawn()` inherits the parent
+/// streams by default, so without this `wait_with_output()` reports an
+/// empty stdout and the `--help`-content assertions panic spuriously.
+/// `Command::output()` pipes for you; `spawn()` does not.
 fn run_cli_or_timeout(mut cmd: Command) -> Output {
     let budget = Duration::from_secs(10);
+    cmd.stdout(Stdio::piped()).stderr(Stdio::piped());
     let mut child = cmd.spawn().expect("spawn fbuild");
     let deadline = Instant::now() + budget;
     loop {
diff --git a/crates/fbuild-packages/src/library/apollo3_core.rs b/crates/fbuild-packages/src/library/apollo3_core.rs
index feae7c5c..597008f1 100644
--- a/crates/fbuild-packages/src/library/apollo3_core.rs
+++ b/crates/fbuild-packages/src/library/apollo3_core.rs
@@ -37,6 +37,26 @@ impl Apollo3Cores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "apollo3-core",
+                APOLLO3_CORE_VERSION,
+                APOLLO3_CORE_URL,
+                APOLLO3_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/arduino_mbed_core.rs b/crates/fbuild-packages/src/library/arduino_mbed_core.rs
index 6567712d..6e0c3e8c 100644
--- a/crates/fbuild-packages/src/library/arduino_mbed_core.rs
+++ b/crates/fbuild-packages/src/library/arduino_mbed_core.rs
@@ -35,6 +35,26 @@ impl ArduinoMbedCore {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "arduino-mbed-core",
+                ARDUINO_MBED_CORE_VERSION,
+                ARDUINO_MBED_CORE_URL,
+                ARDUINO_MBED_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/ch32v_core.rs b/crates/fbuild-packages/src/library/ch32v_core.rs
index 08d5a856..73ff4ba7 100644
--- a/crates/fbuild-packages/src/library/ch32v_core.rs
+++ b/crates/fbuild-packages/src/library/ch32v_core.rs
@@ -33,6 +33,26 @@ impl Ch32vCores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "ch32v-core",
+                CH32V_CORE_VERSION,
+                CH32V_CORE_URL,
+                CH32V_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/esp8266_framework.rs b/crates/fbuild-packages/src/library/esp8266_framework.rs
index 701a0d38..829472cb 100644
--- a/crates/fbuild-packages/src/library/esp8266_framework.rs
+++ b/crates/fbuild-packages/src/library/esp8266_framework.rs
@@ -42,6 +42,25 @@ impl Esp8266Framework {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "esp8266-arduino",
+                ESP8266_FRAMEWORK_VERSION,
+                ESP8266_FRAMEWORK_URL,
+                ESP8266_FRAMEWORK_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/nrf52_core.rs b/crates/fbuild-packages/src/library/nrf52_core.rs
index 80bcec5b..371ee398 100644
--- a/crates/fbuild-packages/src/library/nrf52_core.rs
+++ b/crates/fbuild-packages/src/library/nrf52_core.rs
@@ -33,6 +33,26 @@ impl Nrf52Cores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "nrf52-core",
+                NRF52_CORE_VERSION,
+                NRF52_CORE_URL,
+                NRF52_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/renesas_core.rs b/crates/fbuild-packages/src/library/renesas_core.rs
index 3dac918d..617cfe0b 100644
--- a/crates/fbuild-packages/src/library/renesas_core.rs
+++ b/crates/fbuild-packages/src/library/renesas_core.rs
@@ -37,6 +37,26 @@ impl RenesasCores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "renesas-core",
+                RENESAS_CORE_VERSION,
+                RENESAS_CORE_URL,
+                RENESAS_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/rp2040_core.rs b/crates/fbuild-packages/src/library/rp2040_core.rs
index 12013c60..efd7abee 100644
--- a/crates/fbuild-packages/src/library/rp2040_core.rs
+++ b/crates/fbuild-packages/src/library/rp2040_core.rs
@@ -34,6 +34,26 @@ impl Rp2040Cores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "rp2040-core",
+                RP2040_CORE_VERSION,
+                RP2040_CORE_URL,
+                RP2040_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/sam_core.rs b/crates/fbuild-packages/src/library/sam_core.rs
index 63c36121..1dccfc88 100644
--- a/crates/fbuild-packages/src/library/sam_core.rs
+++ b/crates/fbuild-packages/src/library/sam_core.rs
@@ -33,6 +33,26 @@ impl SamCores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "sam-core",
+                SAM_CORE_VERSION,
+                SAM_CORE_URL,
+                SAM_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/samd_core.rs b/crates/fbuild-packages/src/library/samd_core.rs
index 62ae0e89..189f4113 100644
--- a/crates/fbuild-packages/src/library/samd_core.rs
+++ b/crates/fbuild-packages/src/library/samd_core.rs
@@ -33,6 +33,26 @@ impl SamdCores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "samd-core",
+                SAMD_CORE_VERSION,
+                SAMD_CORE_URL,
+                SAMD_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/silabs_core.rs b/crates/fbuild-packages/src/library/silabs_core.rs
index 3a07ac10..10af6332 100644
--- a/crates/fbuild-packages/src/library/silabs_core.rs
+++ b/crates/fbuild-packages/src/library/silabs_core.rs
@@ -33,6 +33,26 @@ impl SilabsCores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "silabs-core",
+                SILABS_CORE_VERSION,
+                SILABS_CORE_URL,
+                SILABS_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/stm32_core.rs b/crates/fbuild-packages/src/library/stm32_core.rs
index 8354e7b3..86b250f9 100644
--- a/crates/fbuild-packages/src/library/stm32_core.rs
+++ b/crates/fbuild-packages/src/library/stm32_core.rs
@@ -34,6 +34,26 @@ impl Stm32Cores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "stm32-core",
+                STM32_CORE_VERSION,
+                STM32_CORE_URL,
+                STM32_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {
diff --git a/crates/fbuild-packages/src/library/teensy_core.rs b/crates/fbuild-packages/src/library/teensy_core.rs
index 0c785d74..42dd042b 100644
--- a/crates/fbuild-packages/src/library/teensy_core.rs
+++ b/crates/fbuild-packages/src/library/teensy_core.rs
@@ -35,6 +35,26 @@ impl TeensyCores {
         }
     }
 
+    /// Construct with a consumer-supplied override (parsed from the env's
+    /// `platform_packages` line in `platformio.ini`). The default const-pinned
+    /// URL / version / checksum are replaced; `cache_subdir` and `name` are
+    /// preserved. See `PackageBase::with_override` and FastLED/fbuild#681.
+    pub fn with_override(project_dir: &Path, ovr: fbuild_config::PackageOverride) -> Self {
+        Self {
+            base: PackageBase::new(
+                "framework-arduinoteensy",
+                TEENSY_CORE_VERSION,
+                TEENSY_CORE_URL,
+                TEENSY_CORE_URL,
+                None,
+                CacheSubdir::Platforms,
+                project_dir,
+            )
+            .with_override(ovr),
+            install_dir: None,
+        }
+    }
+
     #[cfg(test)]
     fn with_cache_root(project_dir: &Path, cache_root: &Path) -> Self {
         Self {