added advice how to reference existing lambda functions

src/pages/[platform]/build-a-backend/data/custom-business-logic/index.mdx

@@ -184,7 +184,7 @@ export const data = defineData({
 });
 ```
 
-If you want to use an existing lambda function, you can reference it by its name: `a.handler.function('name-of-existing-lambda-fn')`. This references an external lambda resource which Amplify is not aware of. You need to make sure the function and all dependencies are being managed outside of Amplify.
+If you want to use an existing Lambda function, you can reference it by its name: `a.handler.function('name-of-existing-lambda-fn')`. Note that Amplify will not update this external Lambda function or its dependencies.
 
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