How to Add More Combat Static Modifiers?

I want to increase the variety of bonuses that affect each unit type on every terrain. Checking the static_modifiers.txt, I have found that aside from river crossings and amphibious landings, only defending three types of terrain becomes advantageous: hills, mountains, and jungles. I want to give the modifiers of  "defender_bonus" to other forms of geography, like forests or farmland, and to create an opposite attacker_bonus (if it is even possible) for plains, steppes, and desert. Also, in preparation for a possible future personal mod I'm planning, I want to know, is it possible to saddle anti-attrition bonuses for specific terrain on command traits like desert warrior or winter warrior? I will be ratcheting up the attrition in deserts (e.g. Dorne) and in arctic tundra in the far north, then modifying coming of age events that all characters given military training and of appropriate culture (e.g. Free Folk, Dornish, Northmen) will have a large chance of getting Winter warrior or desert warrior. If command traits can be assigned anti-attrition bonuses, then plans can also be made for marshes (e.g. Crannogmen), or mountains (e.g. Mountain Clans). I'm really against the theory of combat in AGOT (from the versions I remember, the ones before 1.5) where gaining a dragon means instant success, while dragon-free combat requires only strength of numbers. I've already increased bonuses for all command traits in other mods (e.g. HIP, CK2Plus) and I want to apply a better military system to AGOT as well.