So I got my Hero last week and am loving it so far, but I'm interested in using the MoDaCo ROM in stead. However, since it's a brand new phone I don’t really want to go and permanently void the warranty straight away. So I was wondering, if I had to return my phone for some reason after switching to the custom ROM, would flashing the official ROM undo everything I'd changed? Or would my carrier/HTC still be able to tell? Thanks for your help EDIT: Oh, and does enabling GPS cost anything?