If the FIRESPOT are not in the model or are called something different, that could be a problem, but not the end of the world.
You could probably get it into fragmotion or milkshape and attatch a firespot to the existing skeleton with out trashing the skinned Mesh. But with out a model program it would be impossible.
Plus x files are pretty hard to change even in the best model programs. Better to take the mesh (.obj) and re animate it the way you want.
There is still a lot you can do with those models from that link with out changing the animations.