Hi there. The mod is a great idea, and I thought you might be fine with some further ideas to add to it. I made the discussion here for such.

My own suggestion would be to allow on creation of a new puppet or dominion the choice to change the main religion of it to your own, or add your primary (first main) culture to its own qaccepted culture list. If a puppet is transferred or freed they lose these changes and revert, except if being played by non-AI in which case a player has the option to keep the religion or culture forced on them.