I have heard numerous stories of pain mysteriously getting better right before surgery. Our feet are evil that way
. Mine did it, and when I mentioned it to my doctor he laughed and said he hears that all the time. Unfortunately I know of no chiropractic adjustment that could heal a tendon. Maybe they can do something that puts less strain on the tendon but I really don't think that your tendon is going to heal without surgery at this point. Once it has progressed to the point of needing the work that you have scheduled it's usually beyond the point of any kind of conservative measure. Wait a few more weeks and see what happens with your pain level. If it's still better you might want to talk to your doctor about it.
but that's just my opinion and I'm not an expert by any means. Just someone who has had PTTD surgery and two other surgeries on the same foot so I've read up ad nauseum on the condition.
Welcome to the board. There is lots of information on here if you do decide to have the surgery.