I'll bet you could even get better readings. Sometimes a proper valve adjustment can improve compression, especially in diesels where a valve with a little more time open can mean more air gets in to be compressed.
All else being equal, a hot motor, with a good tune, at good cranking rpm, can give better readings than a cold one with a tired battery and loose valves.
I suppose you could consider pulling that motor up on deck and giving it a good full-blown tuneup and plopping in back in the boat without doing the "rebuild" thing. I'm sure you could even test run it in the cockpit. Kinda weird though. but that wouldn't stop me
Rus