A few weeks ago, someone else posted on eliminating the DRL's on their Canadian Mustang. I think he ended up giving up on the idea that he could have something flashed/programmed "legally", and ended up buying non DRL headlight assemblies, and an adaptor harness to connect the existing DRL harness to a non DRL headlight assembly.
Otherwise, the dealer can do it, but for a fee. There are dozens of posts on this subject here on this site; they all come down to getting a dealer to turn them off, or replacing the headlight assemblies and buying a harness adaptor to use the late model headlight assemblies.
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.