I kind of like this idea. For one, you can do things easily and wield extra weapons. However, walking around with an arm sticking out of your forehead will increase the weight on the forehead, and your head will probably droop onto your body. I wouldn\'t agree to extra body parts(unless it\'s \'reasonable\'), but I agree with turning your body parts into something else for a limited period of time. I think that the spell should be extremely high in mana, as creatures of evil would be turning their hands into keys/lockpicks and steal everything possible, and nerves in your hand will only make things easier, because you can feel around. Maybe you can tone things down a bit... I don\'t know how for now.
All in all, I am okay with this idea.