It worked with a General Makeup request for me the one time I had PMU. Maybe your parameters weren't met even though it appeared they were? Just a guess.
As far as recycling PMU? - I've never tried but I have been told by someone who has that it works. Drop the trip and pick it back up as normal M/U and your PMU is available again.

I consider that a bit over the line. Definitely not in the spirit of why PMU came to be. It is designed to give someone a chance to make themselves whole after a schedule disruption, not grab multiple trips ahead of everyone else over and over.