While it's not technically game breaking it does effectively break alliance mechanics (by making them completely unreliable and often counter-productive) which is a huge thing in a game where they form a large chunk of the gameplay/strategy.
I do not see a problem with that at all. Alliances should be unreliable because I would think that if you have a new leader from a new family.Why would they keep the same Alliances ?. Why would they have the same goals with those alliances that the previous Royal house did ?. No that makes little sense..It only makes sense if say the same Royal family was the same.But if a new one comes to power why would they keep it ?. but this is my take on it.. I never understood why alliances lasted so long even with a new family on the throne lol. Modern day yes it makes sense.. But in Eu4 era.. I cant understand why it would carry over from one family to the next lol.