If you want to keep your bribed armies, change the export_units_descr file. For each unit, change the ownership to contain the faction that you want.

i.e.

type carthaginian elephant african
dictionary carthaginian_elephant_african ; War Elephants
category cavalry
class heavy
voice_type Medium_1
...
stat_fire_delay 0
stat_food 60, 300
stat_cost 1, 2410, 490, 250, 370, 2410
ownership carthage, romans julii