What I have found out so far - it is possible to customize the default perspective.
What I am missing is a possibility to remove the functionality “Paste -> Paste only contents here” from the documents element tree.
Background information: Our customer has like 20 different employees for content editing. If one of them accidently applies “Paste only contents here” to an existing page, the content of the page is overwritten and the contents are gone. This happened multiple times and therefore the customer wants this functionality to be removed.
What is a possible solution to this problem?