You don't want to install a skimmer that is the wrong size. You *could* cut in a larger one all around if you were changing your liner, but I would not try doing so with an existing liner.
If you have to drill new holes, you are going to have a severely weakened swiss cheese of metal around the skimmer face - an area that is already under a lot of stress. Not to mention the holes also go through the liner.
This is one if the times that I recommend a brick and mortar pool store. Get a piece of thin carboard (a manila folder, the back of a legal pad, etc) and make a template of the screw holes for your skimmer. Then go to a pool store and tell them you need a skimmer that matches.