Sounds like BS to me. I went into my local Timpsons and the guy said they don't do them as the blades can snap in their machine and cause more damage than its worth. So I just went to another and they done it for me with no issues, just that its my responsibility if they damage the blade. Plus even if it did do that to your car (which I doubt) it would still be just as cheap as buying a new key from them in the first place
Doing the mod is easy, just take the transponder out the old key and put it into the new case and secure in with some blutac, I had no problems at all