The smaller the stem and the smaller the tenon, the more difficult replacing it is. (i.e. your pipe & stem would score about an 8 on the difficulty scale)
Be sure whoever you send it to understands that you already had a second stem made, and to NOT modify the shank or mortise in any way to facilitate their re-tenon work. #2 won't fit correctly otherwise.
Finally, I wouldn't recommend mixing tenon materials. Being more elastic than acrylic or vulcanite requires that a Delrin tenon either be larger in diameter or its mortise be smaller to get the same "objective" fit. Achieving a dimensional balance that allows two stems of different materials to be interchangeable would be more a matter of trial-and-error or luck than anything else, meaning the possibility of an unrecoverable BAD outcome would be high. Much safer to make #1's replacement tenon from the same material as #2's integral tenon.
