It docent seem to do that. Here are few things that i know in Viking Invasion Border fort has been given more power and now gan stop several agent. Even really good ones. I just had 7 6star assassins stopped and this got me really curious.

Other agent thing is that what really happens if you bribe enemy castle....I had Citadel bribed and sudently after 2 turns it became Fortress. I didn't mind.
It was pleasant subrice.