diff --git a/README.md b/README.md
index 0491fc6..5ebb322 100644
--- a/README.md
+++ b/README.md
@@ -223,10 +223,11 @@ if native_files_supported() {
 - `sink.rotation` 当前支持 `max_bytes` 与 `max_backups`，提供基础 size-based rotation 和 backup retention
 - `file_sink(...)` 还提供 `reopen()`、`open_failures()`、`write_failures()`、`flush_failures()`、`rotation_failures()`，用于基础可观测性
 - `file_sink(...)` 当前还提供 `append_mode()`；`reopen(append=...)` 在显式传值时会更新后续 reopen 使用的 append 策略
+- `file_sink(...)` 也支持 `set_append_mode(...)`，用于显式修改后续 reopen 将使用的 append 策略
 - `file_sink(...)` 也可直接读取 `path()` 与 `auto_flush_enabled()` 等基础 file 策略状态
 - `file_sink(...)` 还提供 `rotation_enabled()` 与 `rotation_config()`，可直接查询当前 rotation 策略是否启用及其参数
 - `file_sink(...)` 也支持 `set_auto_flush(...)`、`set_rotation(...)`、`clear_rotation()`，可在运行期调整基础写出策略
-- `build_logger(...)` 产出的 `ConfiguredLogger` 同样提供 `file_reopen()`、`file_flush()`、`file_close()`、`file_append_mode()`、`file_path()`、`file_auto_flush()`、`file_rotation_enabled()`、`file_rotation_config()`，以及 `file_set_auto_flush(...)`、`file_set_rotation(...)`、`file_clear_rotation()` 与对应 file failure 计数访问器，便于配置式接入后继续运维控制
+- `build_logger(...)` 产出的 `ConfiguredLogger` 同样提供 `file_reopen()`、`file_flush()`、`file_close()`、`file_append_mode()`、`file_path()`、`file_auto_flush()`、`file_rotation_enabled()`、`file_rotation_config()`，以及 `file_set_append_mode(...)`、`file_set_auto_flush(...)`、`file_set_rotation(...)`、`file_clear_rotation()` 与对应 file failure 计数访问器，便于配置式接入后继续运维控制
 - `sink.text_formatter.template` 当前支持固定 token：`{timestamp}`、`{timestamp_ms}`、`{level}`、`{target}`、`{message}`、`{fields}`
 - 当前可由配置直接组装的 sink 类型：`console`、`json_console`、`text_console`、`file`
 - `queue` 会作为显式包装层附着在最终 sink 外侧；这仍然是同步 drain 模型，不是 async runtime
diff --git a/bitlogger/BitLogger_test.mbt b/bitlogger/BitLogger_test.mbt
index 126f6e8..5c1d80a 100644
--- a/bitlogger/BitLogger_test.mbt
+++ b/bitlogger/BitLogger_test.mbt
@@ -243,8 +243,11 @@ test "configured logger file setters update file sink policy state" {
       queue=Some(QueueConfig::new(2, overflow=QueueOverflowPolicy::DropNewest)),
     ),
   )
+  inspect(logger.file_append_mode(), content="true")
   inspect(logger.file_auto_flush(), content="true")
   inspect(logger.file_rotation_enabled(), content="false")
+  inspect(logger.file_set_append_mode(false), content="true")
+  inspect(logger.file_append_mode(), content="false")
   inspect(logger.file_set_auto_flush(false), content="true")
   inspect(logger.file_auto_flush(), content="false")
   inspect(logger.file_set_rotation(Some(file_rotation(48, max_backups=4))), content="true")
@@ -259,6 +262,8 @@ test "configured logger file setters update file sink policy state" {
   inspect(logger.file_clear_rotation(), content="true")
   inspect(logger.file_rotation_enabled(), content="false")
   inspect(logger.file_rotation_config() is None, content="true")
+  inspect(logger.file_reopen(), content=if logger.file_available() { "true" } else { "false" })
+  inspect(logger.file_append_mode(), content="false")
   ignore(logger.close())
 }
 
diff --git a/bitlogger/BitLogger_wbtest.mbt b/bitlogger/BitLogger_wbtest.mbt
index 48950e8..7d54cee 100644
--- a/bitlogger/BitLogger_wbtest.mbt
+++ b/bitlogger/BitLogger_wbtest.mbt
@@ -124,8 +124,11 @@ test "file sink rotation config normalizes invalid inputs" {
 
 test "file sink setters update auto flush and rotation state" {
   let sink = file_sink("bitlogger-setters.log")
+  inspect(sink.append_mode(), content="true")
   inspect(sink.auto_flush_enabled(), content="true")
   inspect(sink.rotation_enabled(), content="false")
+  sink.set_append_mode(false)
+  inspect(sink.append_mode(), content="false")
   sink.set_auto_flush(false)
   inspect(sink.auto_flush_enabled(), content="false")
   sink.set_rotation(Some(file_rotation(32, max_backups=2)))
@@ -140,6 +143,8 @@ test "file sink setters update auto flush and rotation state" {
   sink.clear_rotation()
   inspect(sink.rotation_enabled(), content="false")
   inspect(sink.rotation_config() is None, content="true")
+  inspect(sink.reopen(), content=if sink.is_available() { "true" } else { "false" })
+  inspect(sink.append_mode(), content="false")
 }
 
 test "file sink tracks rotation failures on unavailable backend" {
diff --git a/bitlogger/README.mbt.md b/bitlogger/README.mbt.md
index 7b45714..bae8a7c 100644
--- a/bitlogger/README.mbt.md
+++ b/bitlogger/README.mbt.md
@@ -222,9 +222,10 @@ test {
 - JSON config uses `sink.rotation.max_bytes` and `sink.rotation.max_backups` / JSON 配置使用 `sink.rotation.max_bytes` 与 `sink.rotation.max_backups`
 - `FileSink::reopen()` can explicitly reopen the current file handle / `FileSink::reopen()` 可显式重开当前文件句柄
 - `append_mode()` exposes the current append policy, and `reopen(append=...)` updates that policy for later reopen calls / `append_mode()` 可读取当前 append 策略，`reopen(append=...)` 会更新后续 reopen 复用的 append 策略
+- `set_append_mode(...)` updates the stored append policy without forcing an immediate reopen / `set_append_mode(...)` 可直接更新保存的 append 策略，但不会强制立即 reopen
 - `path()` and `auto_flush_enabled()` expose core file sink policy state / `path()` 与 `auto_flush_enabled()` 可读取 file sink 的基础策略状态
 - `rotation_enabled()` and `rotation_config()` expose whether rotation is active and which settings are currently applied / `rotation_enabled()` 与 `rotation_config()` 可读取 rotation 是否启用及当前配置参数
 - `set_auto_flush(...)`, `set_rotation(...)`, and `clear_rotation()` allow runtime tuning of core file sink policies / `set_auto_flush(...)`、`set_rotation(...)`、`clear_rotation()` 可在运行期调整 file sink 的基础策略
 - `open_failures()`、`write_failures()`、`flush_failures()`、`rotation_failures()` expose basic sink health counters / `open_failures()`、`write_failures()`、`flush_failures()`、`rotation_failures()` 可用于观察基础 sink 健康状态
-- `ConfiguredLogger` also forwards file reopen, flush, close, append-mode, path, auto-flush, rotation-config, setter, and failure-counter helpers for config-built file sinks / `ConfiguredLogger` 也会为配置生成的 file sink 转发 reopen、flush、close、append-mode、path、auto-flush、rotation 配置、setter 与失败计数访问器
+- `ConfiguredLogger` also forwards file reopen, flush, close, append-mode, path, auto-flush, rotation-config, append setter, policy setter, and failure-counter helpers for config-built file sinks / `ConfiguredLogger` 也会为配置生成的 file sink 转发 reopen、flush、close、append-mode、path、auto-flush、rotation 配置、append setter、策略 setter 与失败计数访问器
 - current scope is observability-first, not a full self-healing sink runtime / 当前定位仍以可观测性优先，不是完整自愈型 sink runtime
diff --git a/bitlogger/config.mbt b/bitlogger/config.mbt
index 3d1cab6..cae5bcc 100644
--- a/bitlogger/config.mbt
+++ b/bitlogger/config.mbt
@@ -239,6 +239,20 @@ pub fn RuntimeSink::file_append_mode(self : RuntimeSink) -> Bool {
   }
 }
 
+pub fn RuntimeSink::file_set_append_mode(self : RuntimeSink, append : Bool) -> Bool {
+  match self {
+    File(sink) => {
+      sink.set_append_mode(append)
+      true
+    }
+    QueuedFile(sink) => {
+      sink.sink.set_append_mode(append)
+      true
+    }
+    _ => false
+  }
+}
+
 pub fn RuntimeSink::file_path(self : RuntimeSink) -> String {
   match self {
     File(sink) => sink.path()
@@ -401,6 +415,10 @@ pub fn ConfiguredLogger::file_append_mode(self : ConfiguredLogger) -> Bool {
   self.sink.file_append_mode()
 }
 
+pub fn ConfiguredLogger::file_set_append_mode(self : ConfiguredLogger, append : Bool) -> Bool {
+  self.sink.file_set_append_mode(append)
+}
+
 pub fn ConfiguredLogger::file_path(self : ConfiguredLogger) -> String {
   self.sink.file_path()
 }
diff --git a/bitlogger/sinks.mbt b/bitlogger/sinks.mbt
index bd70939..8cee663 100644
--- a/bitlogger/sinks.mbt
+++ b/bitlogger/sinks.mbt
@@ -118,6 +118,10 @@ pub fn FileSink::append_mode(self : FileSink) -> Bool {
   self.append.val
 }
 
+pub fn FileSink::set_append_mode(self : FileSink, append : Bool) -> Unit {
+  self.append.val = append
+}
+
 pub fn FileSink::path(self : FileSink) -> String {
   self.path
 }
diff --git a/docs/README-en.md b/docs/README-en.md
index d154c0c..26434c2 100644
--- a/docs/README-en.md
+++ b/docs/README-en.md
@@ -208,10 +208,11 @@ if native_files_supported() {
 - `sink.rotation` currently supports `max_bytes` and `max_backups` for basic size-based rotation and backup retention.
 - `file_sink(...)` also exposes `reopen()`, `open_failures()`, `write_failures()`, `flush_failures()`, and `rotation_failures()` for basic observability.
 - `file_sink(...)` also exposes `append_mode()`. Passing `append=...` to `reopen(...)` updates the current append policy used by later reopen calls.
+- `file_sink(...)` also supports `set_append_mode(...)` for explicitly changing the append policy that later reopen calls will use.
 - `file_sink(...)` also exposes `path()` and `auto_flush_enabled()` for reading basic file-sink policy state.
 - `file_sink(...)` also exposes `rotation_enabled()` and `rotation_config()` for reading whether rotation is active and which parameters are currently in effect.
 - `file_sink(...)` also supports `set_auto_flush(...)`, `set_rotation(...)`, and `clear_rotation()` for runtime policy updates.
-- `ConfiguredLogger` built through `build_logger(...)` also exposes `file_reopen()`, `file_flush()`, `file_close()`, `file_append_mode()`, `file_path()`, `file_auto_flush()`, `file_rotation_enabled()`, `file_rotation_config()`, plus `file_set_auto_flush(...)`, `file_set_rotation(...)`, `file_clear_rotation()`, and the corresponding file failure counters, so config-driven file logging keeps a usable control surface.
+- `ConfiguredLogger` built through `build_logger(...)` also exposes `file_reopen()`, `file_flush()`, `file_close()`, `file_append_mode()`, `file_path()`, `file_auto_flush()`, `file_rotation_enabled()`, `file_rotation_config()`, plus `file_set_append_mode(...)`, `file_set_auto_flush(...)`, `file_set_rotation(...)`, `file_clear_rotation()`, and the corresponding file failure counters, so config-driven file logging keeps a usable control surface.
 - `sink.text_formatter.template` currently supports fixed tokens: `{timestamp}`, `{timestamp_ms}`, `{level}`, `{target}`, `{message}`, and `{fields}`.
 - Config-driven sink assembly currently supports `console`, `json_console`, `text_console`, and `file`.
 - `queue` remains a synchronous bounded wrapper around the final sink, not an async runtime.
diff --git a/docs/changes/0.3.0.md b/docs/changes/0.3.0.md
index 81f9c1b..d27c2b2 100644
--- a/docs/changes/0.3.0.md
+++ b/docs/changes/0.3.0.md
@@ -36,6 +36,7 @@ version 0.3.0
 - feat: add `path()` / `auto_flush_enabled()` on `FileSink` and `file_path()` / `file_auto_flush()` on `ConfiguredLogger` for basic file-policy introspection
 - feat: add `rotation_enabled()` / `rotation_config()` on `FileSink` and `file_rotation_enabled()` / `file_rotation_config()` on `ConfiguredLogger` for rotation-policy introspection
 - feat: add runtime file-policy mutators `set_auto_flush(...)`, `set_rotation(...)`, `clear_rotation()` and corresponding configured-logger forwarding helpers
+- feat: add explicit append-policy setter `set_append_mode(...)` / `file_set_append_mode(...)` so append strategy can be updated without piggybacking on `reopen(...)`
 - feat: add `SplitSink`, `split_sink(...)`, and `split_by_level(...)` for routing records into different sinks by predicate or level
 - feat: add `Logger::bind(...)` as an ergonomic context-binding alias and `fields(...)` helper for tuple-based field construction
 
@@ -56,6 +57,7 @@ version 0.3.0
 - test: cover path and auto-flush introspection for direct and config-built file sinks
 - test: cover rotation introspection for direct and config-built file sinks with and without configured rotation
 - test: cover runtime auto-flush and rotation policy mutation for direct and config-built file sinks
+- test: cover append-policy setter behavior and confirm subsequent reopen calls inherit the updated append mode
 - test: cover split sink predicate routing and level-based routing behavior
 - test: cover `bind(...)` context composition and `fields(...)` helper behavior
 - test: add async logger lifecycle, config roundtrip, and batching/flush policy test seeds
@@ -77,6 +79,7 @@ version 0.3.0
 - docs: document file path and auto-flush introspection helpers
 - docs: document rotation introspection helpers for direct and config-built file sinks
 - docs: document runtime file-policy setter helpers for direct and config-built file sinks
+- docs: clarify explicit append-policy setter semantics for direct and config-built file sinks
 - docs: add split sink examples for level-based routing
 - docs: add `bind(...)` examples for reusable context binding
 - docs: update root README and English README with async adapter notes and current scope