Hi @Henning Svane ,
As stated in the documentation you provided, you could not directly modify the default receive connector, you need to create a new receive connector to do what you expect.
You could refer to: Modify the SMTP banner on Receive connectors
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.