Sure you can always put a larger motor on a smaller pump end. But it will still only pump 1/2HP worth of water. It may work fine for your friend, but it won't lift water from 220' as in your well. A 12 GPM, 1/2HP is only good to about 80' deep and still be able to deliver 50 PSI as needed.
If you want to run a 12 GPM sprinkler zone at 50 PSI from say 250', you will need a 10 or 12 GPM, 1.5HP pump and motor. An 18 GPM, 1.5HP won't work from that depth.