In the normal scheme of things everything is done cold. The chainstay is tapered, drawn, bent, butted (if it is butted), all cold, starting from a solid billet in many cases, and this is considered good for it (it's called "cold working").
Then if it's 853 or 725 or another heat-treated product it's cooked up in an oven and allowed to cool down in a special and carefully controlled way that makes it stronger but less ductile.
You then make it into a frame being careful to only heat it up as much as necessary to weld or braze it together. Generally it gets a bit weaker in the heat affected zone whatever you do (which is partly why you use butted tubes) but Reynolds claims that 631 and 853 get stronger (although they're still butted). How exactly that strengthening works is unclear and it's also unclear how much of it you can expect if you don't just do the normal welding or brazing that the tube is designed for.
So I would avoid any kind of heating. It's possible that you can squash the bit they already squashed a bit more as it will have been normalized by the heating they did. If it doesn't crack it's probably OK. I think you will find that if that that part of the tube has stayed heat treated then it will be very reluctant to deform and if so that's a good time to call it a day and give up before you crack it.