ok, fixed this. But instead of just deleting my whole post I though maybe letting it sit here will help others in the future.
Just out of desperation I just stopped my resilio service again, deleted ALL stuff from /var/lib/resilio-sync and started the service again. Guess what? After having to set the servername/identity new (which makes sense as I just deleted my logs, database config, history etc.) the stuff I put into my config.json is no present in Advanced Preferences and gets used with new shares!
Fair warning, you will lose all your shares of course that way, so you hav