in export_descr_unit change on ownership line it will say

ownership numidia

change to

ownership numidia, carthage*

this can vary between patches, i reccomend finding how carthage is spelt and just copy and paste

then if it fails in descr_model battle, find numidian archers...

and pretty much self explanitory, copy the texture and sprite lines, then replace numidia with carthage or watever