I've peened a couple in the last few years and have yet had one come back to bite me in the butt. That's not to say they're gonna last forever, or a couple of years. Carefully and slowly work your way around as per the instructions above. You dont necessarily have to remove the valve as long as it's seated correctly and squarely. The valve will actually help to keep it in position as long as you do it at TDC.
