Change windows xp sp2 professional key?

I already know how to change the windows xp license key the thing is my version of windows has already been activated and all, but I want to change the licensing key to something else, but it won't let me. Does anyone know of a way to bypass this?Change windows xp sp2 professional key?
http://pcsupport.about.com/od/productkey

Where can I get a feather quilt

speakers won't work