Hello!

I've made some mods for some other games, and thought I might try modding a TW game. I was wondering, how hard is it? Are tools available to make it simpler?
Can you replace models in Rome II with your own? And is it possible to make it so the game is set in a different timespan, such as 400-600 AD? (Mechanics wise, obviously visually that would be done with models and editing the text)