Here’s an interesting modification for a Guitar Hero controller. An anonymous modder posted a project to Instructables showing how to convert a full size controller to a small size. The modder converted his to a smaller size for his two year old daughter, but whatever your reason is, it looks like a fairly easy thing to do.
Seems like a fairly rudimentary project, all you need is a Torx screwdriver, a small Phillips head screwdriver, a hacksaw, some glue, and some mending plates. You then take apart the donor guitar and perform the necessary surgery to make the neck smaller based on your particular needs. Of course it’s a bit more complicated then that, but feel free to read over the full instructions posted by the author.