I too have a similar problem.

I've tried to move Byzantine cavalry over to being a militia unit in towns, editing my EDB so that they should be recruitable in any town with stone walls or better. The game doesn't crash, nor does it allow me to recruit them in any fashion except in castles still.

I've noticed that modding the EDU file for unit stats also does nothing to the units in game. I've tried modding unit size and their weapon and armor stats but it does nothing to the game.

Why don't these files work?