I'd say it really depends upon how far off it is. If the adjustment is less than 2cm, I'd say it's OK to bend it back. If it's more, I'd worry about the amount of stress needed. You see, in order for the fork to take a permanent bend in the first place, you have to exceed the material's yield-strength. Then to fix it, you have to exceed it's yield-strength a 2nd time in the opposite direction, very scary.
Also in general, the stronger the alloy, the closer yield-strength comes to ultimate-strength. By the time you apply enough force to make a bend stick, it's also very close to breaking.