The ally system in M2TW is fairly basic - very few advanced or interesting features. Specifically, I think a useful addition would be to add a mechanic where you can ask an ally to attack a specific army or take a selected settlement, and based on your relations with that faction and the difficulty of the task they will accept or decline. Other possible ideas would be having dual garrisons; where you can send your troops to enter friendly control in either a settlement or an army, and until you remove them they are under allied control; and vice versa. Any other plausible ideas you can come up with would be useful as well. I have searched for some time and I haven't found any mod quite like the one I'm suggesting so unless someone corrects me, I'm going to assume there isn't one.

Because I have never modded any Total War game I can't accurately judge how difficult if possible it is, so therefore I would like to know if it is and then either someone who can mod make it or inform me of how to do so.
And as a final request, if there is anyway it can be compatible with the Third Age mod, that would be excellent.