You can't turn them into polybian ones but you can still retrain them at the "old" barrack.

Camillan Triari looks cooler also having Mars [I'm not sure but unlikely Medusa] head on the shield.

but capable to slice phalangitai piecemeal
Well I wouldn't call it "piecemeal" but yeah I notice I don't have to pin Elite African Pikemen on all four sides anymore to kill them...