copy the whole of the imperial campaign folder and then rename that and then copy all of the base folder and put that in the new imperial campaign folder... delete map.rwm then make your changes if you have removed any factions get rid of them in the playable/non-playable place make sure you have asigned all the provinces to a faction then start a new game and in the single player menu there should be a 'provincial campaign' choice and use that....

btw i am not sure if you can get rid of the senate though so just have one roman factoin and a senate...

GMM