"Don't enter the setup room!" really is not a sufficient or acceptable answer. The OP said it is a custom figure, which often requires additional bones, and there's no other way to add those bones without entering the setup room unless you're doing it in a text editor. I have the same issue when I'm working on figures but I thought it was only with weight mapped figures. I've gone into the setup room to add bones to the neck or abdomen, and then again to add bones to the face for facial rigging, and every time I do I have to repaint weight maps in the jaw bone. They also don't mirror correctly even though the mesh and the bone joints are 100% symmetrical, so I have to get them close to mirrored by hand.