I've done it a few times, although not usually for a mistake. If I have a half used film in the camera that needs to be pushed, say, and then next time I use the camera I know that pushing would be the wrong way to develop, then sometimes I'll cut the film in two. Works best for 35 mm because you can rewind the film, then reload in the dark room and shoot off as many shots as you need with the lens cap on and then open the back (in the dark) and cut reasonably accurately in the right place. Roll film is a bit harder because it is more difficult find the right place and obviously you don't want to cut through the frame you are trying to save.
Originally Posted by Jarvman
Of course, the shot that you put the scissors through is ALWAYS the best shot on he roll