Changing settlement occupy/sack/raze permissions by faction?

[Geleco]

I want to make it so that the Celtic and Norse factions can only sack. I don't want them to be able to capture cities. It just looks dumb to have Picts roaming around the Mediterranean conquering a patchwork of cities. But looking in the files, the only way to change occupation options is by culture. Is there a way to change it by faction so I can make only these 6 unable to occupy/loot?

[SharpEyed]

hmm, both Celts and Norse factions are subcultures of Barbarians, however Alamans Langobards etc too

changing it by faction? hmm not that I know of, only way would be the changing some sub-cultures (assign them to other culture something) but I think this might need you to create a new culture something..
because most likely diplomacy etc will be messed up