That's a good suggestion, however I really want to keep the Romano-Brits in there. I'll keep on searching.
UPDATE: it works, it works!!!
The Eastern Roman Rebels are now the Romani Pretenders, and the Western Roman Rebels are out of the game. I just added the shadow faction trait twice in descr_sm_factions.
The great thing is now I can add the Moors and rename them 'Arab and have them harry the Eastern Roman Empire from the start, making them a little less prone to domination.
UPDATE 2: There is a downside to this, which I should've thought of, of course: when one of your provinces rebels and defects to the Romani Pretenders, and they can't get the rebellious city under control and it rebels again, there's a 50% chance it will revert to a different Roman faction than it originally was a part of. An example: all the cities of the Iberian peninsula rebelled against the WRE, but when the loyal citizens of Corduba rebelled against the Roman Rebels, there was a loyalist revolt and the city went to the ERE!!! Lol. Gotta find something for that...
[This message has been edited by jgenard (edited 10-07-2019 @ 04:27 PM).]