99.999% of all of the springs I've designed, and ones designed before me, and so on are totally special for the applications they are use in. Yes, I try to pick a stock one, lots of times that won't work for one reason or another. For a prototype, I've actually gone down to my local True Value hardware store and picked up several in their selection to try. Modified many to work for our needs. Never re-heat treated any of them after reforming the ends to work. If the prototype spring worked, then the design was sent to our favorite spring vendor and made in larger quantities for production. So, I guess to answer what the OP was asking, I personally don't see a need to re-heat treat a spring after modifying. The most would be to re-temper the area of change, drawing it to a temperature of the color of the spring material as described above and call it good. Ken