Is there a way to designate computer-controlled sovereigns (custom or not) to automatically belong to custom factions I've created, every time I start a new game?  In other words, I want my custom sovereigns to belong to custom factions I've made (while selecting rival factions at the start of a new game), instead of simply joining random factions with no control over which one they end up in whenever I start a new game.  I expect it's a pretty simple thing to do, but I cannot figure out how to pull this off.  Hope I'm being clear enough.

Either way, I firmly believe this feature should be a basic option plainly displayed while creating a sovereign; freely being able to select a faction they belong to, so that AI can easily assign them to the specific faction when they are selected as opponents in future play sessions.