Player-Only Custom Kingdoms & Empires
This mod changes the "Found Kingdom" and "Found Empire" decisions, preventing the AI from taking them and messing up the de-jure borders. The game unfortunately only has a game rule to do this for duchies.
Crusader Kings III Mods Catalogue
This mod changes the "Found Kingdom" and "Found Empire" decisions, preventing the AI from taking them and messing up the de-jure borders. The game unfortunately only has a game rule to do this for duchies.