Re: New Pickguard Replacement
How close are the two holes?
Unless they are really right next to each other, I'd try installing it by drilling a new hole, and seeing what happens. If it works, leave the old hole alone. If it doesn't, then fill the old hole with any number of things. I prefer to drill and dowel, myself. You can get poplar dowel rods for dirt cheap at any hardware store. Use a small miter box and a small hand saw to cut the length of dowel you need (should be around 3/8").
Make sure that the drill bit you use to make the new screw hole is the width of the core diameter of the pickguard screw. A common mistake is to use a drill bit that is about as wide as the thread diameter. That creates an unnecesarily large hole, and gives the threads very little wood to bite.