I'm no 853 expert but I don't know of anyone who heats a bike tube (of any kind) before they manipulate/shape it. If the shop that did the repair will back the stays (now that they have been shaped against Reynolds's guidelines) then leave them as is and run a narrower tire if the clearance needs it. If the shop won't give a warranty then do what you wish as you'll be the only one who cares.

I do have questions. Did you specify the CS brand/material? Did you have a discussion about other issues like tire clearance prior to the work? Did the shop offer any suggestions?

Since the OEM stays failed from a incident creating a stress riser it seems to me that they were strong enough to work under "normal" conditions. The 853 might be stronger but they might have less elongation and, if of thinner wall, have less of a fudge factor to deal with the next incident. Andy