Site Members Request: Customizing the Restricted Access Page

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Currently, it is not possible to customize the page that site members see when they try to access a page that they do not have permission to access, e.g. members-only pages or private pages. 
notification saying 'you don't have permissions to access this page'
Customizing the restricted access page would let you add your own message to the page to explain how members can get access.
We are always working to update and improve our products, and your feedback is hugely appreciated.