Please just read my posting.
I did it and it's kind hard to understand.
... sorry, then because of my own German to English translation 😢
But few minutes ago I stopped the synchronization on my home/private PC, deleted all bookmarks (first only into recycle bin), restarted Opera and activated the synchronization again – because I cleaned up some of the "merged" 😞 bookmarks on my office PC this week. After waiting several minutes (only a very small exclamation mark signaled that Opera was doing something: http://www.abload.de/img/2017-07-22_shot_00145ubp.jpg) now I have the same bookmarks of my office PC.
Hopefully Opera will not reanimate my deleted old bookmarks on my home PC...