Not sure what you are getting at.
But here goes.
All the animations are hard coded into the game, and we have no way of changing them, or add new ones. So if you want to alter the animations for the stances you're all out of luck.
Are you wondering how you define the soldier as an MG gunner, it has to do with the config.cpp. I suggest you check out Addons: General for help with config.cpp.
Cheers, KTottE