Typically it's not a good idea to change the pump on a skimmer. They are usually sized to match what the body can handle. Some people do upgrade the needle wheel by adding some Enkamat mesh to make a hybrid mesh wheel. This will help the pump make finer bubbles and improve the skimmers performance. Besides, there are good makes of skimmers on the market that only cost a few dollars more than a quality pump alone.
Hope that helps.
