Yes, it's easy enough to change the reading. But the reading on the hour meter doesn't tell you how the tractor was maintained, or how hard it was worked, only that the key was in the "on" position for so many hours. Personally, I'd rather buy a tractor with 3000 hours that had the oil changed every 50 hours, than one with 500 hours that had the oil changed twice, for example. If you're concerned the hour meter might not be accurate, look at the wear points, like pedal bushings, 3 point link bushings and pivots, etc., they shouldn't show noticeable wear on a 500 hour tractor, unless it's been treated like a rental. In my experience, you get more information by weighing the words of the former owner, than by looking at the tractor.