diff --git a/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/README.md b/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/README.md
index 0c01125e5cec..54518fa86d02 100644
--- a/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/README.md
+++ b/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/README.md
@@ -119,13 +119,17 @@ Lists all available analyzers in your Microsoft Foundry resource. Shows how to d
 ### Sample 08: Update Analyzer
 
 #### `sample_update_analyzer.py` / `sample_update_analyzer_async.py`
-Updates an existing custom analyzer's description and tags. Shows how to modify analyzer properties.
+Updates an existing custom analyzer's description and tags. Only `description` and `tags` can be updated
+with `update_analyzer`. Use `begin_create_analyzer` with `allow_replace=True` to change create-only
+properties such as `models`, `field_schema`, `config`, `dynamic_field_schema`, `processing_location`, or
+`knowledge_sources`. If `base_analyzer_id` is included in an update request, it must match the existing
+analyzer.
 
 **Key concepts:**
 - Updating analyzer description
 - Adding, updating, and removing tags
 - Verifying analyzer updates
-- Modifying analyzer properties
+- Replacing create-only analyzer properties with `begin_create_analyzer(..., allow_replace=True)`
 
 ### Sample 09: Delete Analyzer
 
diff --git a/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/async_samples/sample_update_analyzer_async.py b/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/async_samples/sample_update_analyzer_async.py
index 84fefbc0d401..9d866fe20cda 100644
--- a/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/async_samples/sample_update_analyzer_async.py
+++ b/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/async_samples/sample_update_analyzer_async.py
@@ -11,11 +11,15 @@
     This sample demonstrates how to update an existing custom analyzer, including updating
     its description and tags.
 
-    The update_analyzer method allows you to modify certain properties of an existing analyzer.
-    The following properties can be updated:
+    The update_analyzer method allows you to modify only these properties of an existing analyzer:
     - Description: Update the analyzer's description
     - Tags: Add or update tags
 
+    To change create-only properties such as models, field_schema, config,
+    dynamic_field_schema, processing_location, or knowledge_sources, use begin_create_analyzer
+    with allow_replace=True. If base_analyzer_id is included in an update request, it must
+    match the existing analyzer.
+
 USAGE:
     python sample_update_analyzer_async.py
 
@@ -94,7 +98,9 @@ async def main() -> None:
             tags_str = ", ".join(f"{k}={v}" for k, v in current_analyzer.tags.items())
             print(f"  Tags: {tags_str}")
 
-        # Create an updated analyzer with new description and tags
+        # Create an updated analyzer with the properties supported by update_analyzer.
+        # Keep base_analyzer_id unchanged; other create-only properties require
+        # begin_create_analyzer(..., allow_replace=True).
         updated_analyzer = ContentAnalyzer(
             base_analyzer_id=current_analyzer.base_analyzer_id,
             description="Updated description",
diff --git a/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/sample_update_analyzer.py b/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/sample_update_analyzer.py
index 70b1410f419f..f72b89fe32a8 100644
--- a/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/sample_update_analyzer.py
+++ b/sdk/contentunderstanding/azure-ai-contentunderstanding/samples/sample_update_analyzer.py
@@ -11,11 +11,15 @@
     This sample demonstrates how to update an existing custom analyzer, including updating
     its description and tags.
 
-    The update_analyzer method allows you to modify certain properties of an existing analyzer.
-    The following properties can be updated:
+    The update_analyzer method allows you to modify only these properties of an existing analyzer:
     - Description: Update the analyzer's description
     - Tags: Add or update tags
 
+    To change create-only properties such as models, field_schema, config,
+    dynamic_field_schema, processing_location, or knowledge_sources, use begin_create_analyzer
+    with allow_replace=True. If base_analyzer_id is included in an update request, it must
+    match the existing analyzer.
+
 USAGE:
     python sample_update_analyzer.py
 
@@ -92,7 +96,9 @@ def main() -> None:
         tags_str = ", ".join(f"{k}={v}" for k, v in current_analyzer.tags.items())
         print(f"  Tags: {tags_str}")
 
-    # Create an updated analyzer with new description and tags
+    # Create an updated analyzer with the properties supported by update_analyzer.
+    # Keep base_analyzer_id unchanged; other create-only properties require
+    # begin_create_analyzer(..., allow_replace=True).
     updated_analyzer = ContentAnalyzer(
         base_analyzer_id=current_analyzer.base_analyzer_id,
         description="Updated description",
diff --git a/sdk/contentunderstanding/azure-ai-contentunderstanding/tests/conftest.py b/sdk/contentunderstanding/azure-ai-contentunderstanding/tests/conftest.py
index 70599b28e003..194281c87674 100644
--- a/sdk/contentunderstanding/azure-ai-contentunderstanding/tests/conftest.py
+++ b/sdk/contentunderstanding/azure-ai-contentunderstanding/tests/conftest.py
@@ -111,6 +111,11 @@ def add_sanitizers(test_proxy):
         value="https://Sanitized.services.ai.azure.com",
         regex=r"https://[a-zA-Z0-9\-]+\.services\.ai\.azure\.com",
     )
+    # Keep playback stable when recorded endpoints include a trailing slash.
+    add_uri_regex_sanitizer(
+        regex=r"//contentunderstanding",
+        value="/contentunderstanding",
+    )
 
     # Sanitize Ocp-Apim-Subscription-Key header (where the API key is sent)
     add_header_regex_sanitizer(key="Ocp-Apim-Subscription-Key", value="fake-api-key", regex=".*")