Never, ever, ever, ever, ever copy joints. It just... doesn't work.
2)You don't actually change the joint's name, but rather, you change the joint's controller. Open the UI (the button is on the same toolbar as play/pause) and select the joint you want to change. In the box labeled 'controller', remove the joint's name and type something else. That is what the slider controlling it will then be called. To control two things with the same name, just type the same controller. The joints don't have to be the same kind for this to work. I hope this helps!