I do that. I use a function generator on sine and set it to the free air re sonance frequency It is easy to see, whatever frequency moves the cone the most. Then I see which way it might have to go to be in the most perfect ce nter. It could be fine without touching it but I push it both ways on both axes to find which way the bent bends. Whichever way I got the most clearan ce before the voice coil rubs is the direction I "coax" it to before the gl ue dries.
Once I had to fix one someone else had done. He thought it would require re moving the glue and tearing everything out. Nope. I simply bent the frame s lightly. Of course this will not work on speakers with cast frames so just be more careful on those.
Actually there is money doing that. I heard of a guy in my state who starte d doing a few and still worked. In a couple of years he quit his day job to do this full time and makes decent bucks doing it. He can't keep up with t he work. I am considering doing it. All you need is a little bit of exposur e and a few satisfied customers. And of course I would have a discount for cash... It would tie in nicely with any of my stereo fixing endeavors as we ll, it would be practically the same customers. And audiophiles go in packs , at least on the internet. Of course some of them will fly cross country t o hear another's system, but when your system cost more than a new car you do things like that.