Regarding the Emperor of California suddenly turning into a theocrat, you'll need to bar the Empire of California title from using the Theocracy government type, as well as rigging it to be allowed to use Feudal. Also, you may want to consider making a special government type for the Emperor, High Chairman, High Fabricator, and Fylkir that allows them to hold Temples so that their religions can benefit from the religious head controlling a holy site. Also, it may be amusing to give the Consumerists a feudal government type that doesn't let them hold castles, and instead gives them cities without penalty.
The other, somewhat less serious suggestion I have is a special government type for the President of the Americanists that uses decadence. Rename decadence to "Approval Rating" and cancel out its affects on demesne. It could be entertaining to have various events fire depending on the President's approval rating, with good things happening from it being high, and bad things from it being low. Perhaps if it gets low enough, other Americanists could pressure the President to resign from office triggering a new election.