I have a few new animations in Stormworld, not for humans though. I used 3ds max, but Maya and Blender should work just fine.

Yes, it is possible to implement new animations everywhere. The only limitation is that animations are bound to different events - a unit's Death, it Idling, it Running and so on. This makes it not possible to create a new animation set for dual wielding daggers, for example (except if you have a unit that only does that).

A word of caution, creating animations is extremely time consuming and difficult. I would be surprised if they hadn't spent thousands and thousands of hours to create the ~900 animations currently in the game.