Inplace Upgrade also works, just tested under Windows 10 Pro 19042.804 on 19043.844 X64. And it goes very quickly, less than 10 minutes.
Downgrade seems to work too from 19043.844 to 19042.804 I'm on it. Edit: Downgrade worked with Personal files and Apps. I'm back on 19042.804.
Added the latest SSU to the mirrors: https://forums.mydigitallife.net/threads/windows-10-hotfix-repository.57050/page-588#post-1645340 And now i am off to bed