It's possible to cause a region to change realms with diplomatic actions alone (if your diplomat can avoid being arrested) but I can't remember whether it's possible to perform those in a rogue region.
The religious equivalents only change sentiment towards the realm controlling a region so I wouldn't expect them to cause a rogue region to join a realm.
And RTOs are one of those features that make perfect sense when you play a priest and have had to work hard preaching to get the necessary level of religious support, but to everyone else look like instant magic and totally unfair.
Now I need a rogue region to play with so I can play and find out for sure.
