docs(repository_custom_properties): clarify non-authoritative behavior and import management

Author: mkushakov

website/docs/r/repository_custom_properties.html.markdown

@@ -9,6 +9,8 @@ description: |-
 
 This resource allows you to manage multiple custom property values for a GitHub repository in a single resource block. Property values are updated in-place when changed, without recreating the resource.
 
+~> **Note:** This resource is **non-authoritative**: it only manages the custom property values explicitly declared in the `property` blocks. Any other custom properties set on the repository by other sources (UI, API, or other tooling) will be ignored and left unchanged.
+
 ~> **Note:** This resource manages **values** for custom properties that have already been defined at the organization level (e.g. using [`github_organization_custom_properties`](organization_custom_properties.html)). It cannot create new property definitions.
 
 ~> **Note:** This resource requires the provider to be configured with an organization owner. Individual user accounts are not supported.
@@ -77,14 +79,14 @@ In addition to all arguments above, the following attributes are exported:
 
 ## Import
 
-Repository custom properties can be imported using the repository name. When imported, **all** custom property values currently set on the repository will be imported into state.
+Repository custom properties can be imported using the repository name. When imported, **all** custom property values currently set on the repository will be imported into state. After import, only the properties present in your configuration will continue to be managed; any properties not declared in `property` blocks will be ignored on subsequent plans.
 
 ```
 terraform import github_repository_custom_properties.example my-repo
 ```
 
 ## Differences from `github_repository_custom_property`
 
-This resource (`github_repository_custom_properties`, plural) manages **all** custom property values for a repository in a single resource block, with in-place updates when values change. This is useful when you want to manage multiple properties together as a unit.
+This resource (`github_repository_custom_properties`, plural) manages **multiple** custom property values for a repository in a single resource block, with in-place updates when values change. It is non-authoritative — only the properties declared in the configuration are managed. This is useful when you want to manage multiple properties together as a unit without affecting properties managed elsewhere.
 
 The singular [`github_repository_custom_property`](repository_custom_property.html) resource manages a **single** property value per resource instance. Use it when you need independent lifecycle management for each property.