I'm not really sure that the game needs card abilities to be converted into game rules. There is already enough to consider during a given turn, some of which can be confusing, and having to remember that these options exist and all the specific restrictions (once per game for Retreat, removing them from the game after battle for the Ambushers, etc.) would just end up creating more complexity without adding any significant (in my opinion) diversity to the game.
I think these are interesting ideas to build into cards (a territory-class enhancement that provides the Retreat effect, for example) but I don't think they should be game rules.
