Does the "no vassal count or above has a negative opinion about you" requirement count all vassals, regardless of Kingdoms? It doesn't make much sense that it would (why would it matter that the count of Kent doesn't like me if I'm trying to change the succession laws of Norway?), but it seems to be the case. Either that, or it counts all vassals, including the count vassals of your dukes. Because I've gone through the vassal list, mildly bribing a few people, and the only people who dislike me are a few imprisoned dukes in England. Do I really need to mollify them to be able to change the laws of Norway?