Cid & Mid Question

I'm looking at changing my Cid which is currently uk orange to htc generic Europe. I'm a little confused as well as my CiD do I need to change the Mid as well. I can't find any reference to which CID goes with which Mid if I need it. Any help would be appreciated thanks

from xda-developers http://ift.tt/2aKozA2
via IFTTT