Hello, is there a possibility to delete all unneeded values / fields when saving a page? I found the cleanup.php script, but I think that can be solved by a hook. I am open for any idea. 
Yes, you can do that with a page.update.after hook (and/or changeStatus etc). But usually, you would have to do this only once after you made changes to blueprints, so I wonder if waiting for page changes is the way to go here.