Sounds like you can get the piece of frame off the cabinet if you are thinking of using a table saw. To remove 1/2" from the frame I think you'd be happier with the results if you used a planer. Might take a couple passes to get the full 1/2" but it would look very good once done. Just make sure you remove ALL the nails/brads/stables before sending the piece through.
Good Luck.