I would seriously doubt if there is anything illegal about changing an hour meter. Is there any other equipment that is subject to smashed hour meters, whether intentional or not, than forklift trucks?
It would seem that if there is a problem with changing hour meters that when you buy a new one that you would have to certify what the make model and serial # of the truck that it was it was installed on and register that with some governmental authority.
Like all things, it is a matter of trust combined with knowledge. When you see an ad in E bay or Craigs List that says a truck is a 1993 and you know that the truck was discontinued in 1985-is that illegal or just an oversight by an uninformed seller.
How about the guy in NY that advertises that "if you bought the same used truck" that he is offering from a "dealer" that the "dealer" would charge you X, which is more than list price of a new one. Unfortunately, those who tell an uninformed customer what they want to hear thrive in an economy like this. It's too bad.