Changing the leader battle models...?

:beam: I would greatly appreciate the help of anyone who would tell me how to go about changing the battle model for a faction leader or general...

Simply put...the only thing I want to change about the game is the way they all look the same and wear complete plate armour. My goal is to have them all look like the same model of Duke William in the prologue...

From what I understand this shouldn't be a very complicated thing to do compared to all the other stuff that I've glanced through on here about modding...so can anyone help me out with a short and simple walkthrough on this? :beam: