I have two separate suggestions for the game
1) Change Varangian adventure white peace outcome
So I suggest that when you go on varangian adventure (for example as Hrolf against France over Normandy) if none of the sides can exactly acquire decisive victory - in case of white peace Viking invader gets the title, remaining a vassal under King/Emperor and changing faith to his Liege's. This will represent the historical outcomes of varangian adventures more accurately.
2) Implement parental cultures
So there are some cultures in the game that represent more of a generic conglomerate rather than specific cultures. I'm talking about Russian, Norse or German cultures for example. These cultures should have easier time splitting, but also if you're powerful lord, you should be able to unify minor cultures into one parental culture.
1) Change Varangian adventure white peace outcome
So I suggest that when you go on varangian adventure (for example as Hrolf against France over Normandy) if none of the sides can exactly acquire decisive victory - in case of white peace Viking invader gets the title, remaining a vassal under King/Emperor and changing faith to his Liege's. This will represent the historical outcomes of varangian adventures more accurately.
2) Implement parental cultures
So there are some cultures in the game that represent more of a generic conglomerate rather than specific cultures. I'm talking about Russian, Norse or German cultures for example. These cultures should have easier time splitting, but also if you're powerful lord, you should be able to unify minor cultures into one parental culture.