To remove Augustan reforms and trade them for new units for new factions is an excellent idea!!! (otherwise why should we have new factions?) It is a matter of ballance - it has nothing to do with whether one likes the imperial units or the Roman Empire or not. Simply, given a certain number of unit slots and increased nuber of factions, it is only natural that some old units will have to go - and the augustans seems the most natural candidates for that, especially given the fact that they came so late in the game and that S.P.Q.R. have polybian and marian reforms already.

I think, however, that it will still be nice to leave the Imperator trait (and some nice ancillary maybe) in place and make it hereditial just for role-playing purposes.

As to the skins idea, I am afraid that it will not work, beacause the skins are defined by the faction ownership and here we would have two different skins for the same unit owned by the same faction, which is probably impossible.