Yes, many people have asked this and just so you know you can use the handy Search Button to find these topics before posting a new one
But, to answer: Changing a model is immensely difficult. RIght now there is not much support on the matter because few people have managed it and only with lots of careful editing and trial and error. If you want to try yourself, you can try such programs as blender and nifskope, but it isn't something that's going to be easy.