There are products for repairing threads. You can normally find these products at auto part stores. Here in Canada, I've seen them at the automotive section of a store called Canadian Tire.
I've never actually used or purchased a thread repair kit but I did read the packaging once while shopping. They work like this, you fill the damaged threaded hole with the thread building compound, then you coat a screw with the provided release agent, you screw the screw or bolt into the hole, wait for it to cure and then you can remove the screw and there will be threads left behind in the hole. I think this kind of product might work for rebuilding the threads on a flashlight but I can't guaranty that it will.
http://www.accessconnect.com/loctite_threadlocker_.htm
The first product on this page is the stuff I'm talking about. You might even find it at walmart.
If you screw up your light or glue it together permanently, I assume no responsibility.