They will insist upon the conversion if you send it in. Period. Just be sure they return your original parts so it can be reconverted in the future if you want.
There is one advantage -- the hammerblock version is a safer revolver. I know, I know -- the old version, properly used, is perfectly safe. But the hammerblock guns can be carried fully-loaded and abolutely cannot fire unless the trigger is pulled.
Some dislike the trigger feel of the conversions. To me, they do feel a bit heavier, but are not as heavy or different-feeling as the New Models.