Head Armor is, as it says, for the head protection. Additional dmg would only cause one thing:
All Archers, Crossbows or anything else for range dmg goes with that additional dmg and gets a buff. All infantry do need their head armor and cant use it unless they want to die very easily in melee...
Also dont like the idea of it, however wouldnt be opposed (as Im fine with archer buff)
This is a good point, but realistically face paint can't give any sort of head armor, that just wouldn't make sense lol, so it had to be something else.
Having war paint on a face is likely to make people look more intimidating or make them
feel more patriotic in the cause and buff them in some sort of fashion.
For a crossbowman melee is a much greater possibility and 1-2 damage increase on an already huge pierce base value doesn't sound totally absurd for losing his helmet. I'm not sure how much more damage an archer is going to do with a couple extra damage points.
Just needs to be something unique that it offers otherwise equipping it is pointless and you'd be better off with a woolen cap for it would offer more protection. The main thing here isn't to break the balance but to have face paint!