Sounds very interesting. For M2, the mod switch is now standard (and indeed pretty much the only option) have a look here:
https://forums.totalwar.org/vb/showthread.php?t=73971

I would recommend you try out the mod switch and then think about how that fits in with your ideas.

Alternatively, have a look at these texture files:
https://forums.totalwar.org/vb/showthread.php?t=74083

If you can write a programme that converts the .tga file into the .texture file and get new textures in game then you will receive many awards and praise from the community.