Don't bother. It'll be hard and you can't do much. The thing you'd do is edit the resource fork with ResEdit or, if there is no resource fork, find the resource file, use some utility to swap it from being in the data fork to the resource fork, edit it, and then convert it back. So, if you haven't used ResEdit, there isn't a whole lot that you can do. You can change some strings in the program, you can change the window type, maybe move around a few UI elements but that's about it.