I have a "Razer" Deathadder mouse and I was trying to map the 2 side thumb buttons and the game would not let me. I was curious to know if there was a way to do this?

There is no way that I know of, they left the game saddled with very few ways to map the keys, it is just plain lazy if you ask me. I would love a mod that allowed it but if there is one I have not found it.