If we are talking clock mainsprings then no I don’t believe you can. Not saying it is impossible but when you can buy them for a few dollars your time trying this procedure from a business stand point is not worth it. I asked my old mentor (70 yrs of watch and clock repair) who has since passed about this 25 or so years ago. He told me that you would have to get the spring heated evenly across the length and then stretch it out to reheat for hardening which he said would be next to impossible. Just some of my thoughts.