The difficult part about priests siezing regions, and which troops do and don't try to arrest, is that there is no way for a realm to specify *which* TOs it would allow, and which not. Let's say a VE priest joined Astrum and tried to do a TO of an Aurvandil region. There's no way Astrum would sanction that and allow it to happen. So of course we would stop him. Without any way for the game to tell what is OK and not OK, then either way there will be bad situations that don't match what the players would expect to happen.
So we could allow a game-mechanic official religion with no real in-game effects except solving this problem and being listed on the realm info page.
