The way I understand it is you can change any part of a fixture location etc BUT you can't add additional items I.E an extra socket or you can but you then have to get it certified by a qualified electrician, your right to check as people will be all for it at the time to save them a sparky but if anything were to go wrong they would be only to quick to point the finger at you!

I two would like to know the certain answer to this.

Martin