Bending the butt plate for other than squaring up the butt plate it self it shouldn't have to be annealed in my experience to make small adjustments to the contour. Some castings have a twist in them, if its a lot send it back to get a replacement. I like cleaning up the casting making it square then getting the wood off that doesn't belong. I like to peen the butt plate in the final phase of the job and tap it home to close up any small gaps along the edges after I get my screws in place. As your inletting improves you will have less peening needed in the end.
