Limiting units per army

[Vitoria90]

So I've asked around a few places already, and I suspect this might be impossible, but doesn't hurt to ask.

I want to mod a unit limit that is army based into the game, as opposed to global. This limit would impede players as well as AI from spamming any singular unit and would make the higher tier units more special but it would let every army have them. Anyone have any clue how this could be done? I don't mind if it's done through character skills or some overall code, so long as it works, or if it locks out unit recruiting after a limit or maybe makes further recruited units get higher upkeep (a bit like Bretonnia and its vows).