How difficult is it to create a game modification for 0 A.D.? Is there a guide where to start? Things I would like to do include changing unit statistics (e.g. health, armour, training time), introducing new unit types, overhauling the damage counter system, and adding six new factions (Armenia, Attalids, Boeotians, Parthia, Ponthus, Scythians) but reusing the existing graphics etc. Any advice or help to get started would be appreciated.