First, let me say, I ain't no attorney (IANA), and maybe for legal questions you should consult a real attorney.
Forklifts do not come under "motor vehicle" laws, but do come under manufactured goods laws.
Just like ANYTHING you sell or purchase, there is a responsibility that what you sell, is actually what you said it was, so there is fraud if someone -intentionally- changes the hour meter, and claims in the sale that the truck is younger/newer than it really is. How much that fraud was worth, decides if the fraud reaches a level of "felony", and that varies state to state.
And the big "if"; if it can be proved to have been done intentionally to fool the buyer, not just as "a year ago the hour meter broke and was replaced, we used to have a sticker telling us how many hours the old meter had, but it got painted over".
There is no rule as far as I can see on itsdf.org saying an hour meter is a -required- item on a powered industrial truck.
As far as "do nothing", why don't you just make a sticker and put it on the truck near the hour meter. I just write a plus sign and the old hour meter reading (so if you ever see a forklift with a foil sticker near the hour meter that says "+2345" you can know I saw that unit, changed the hour meter or dash panel and that truck had 2345 hours when I changed the hour meter.
Have you heard about the "newest" idea about that, since the hour meter reading in new trucks are held in the computers, when ever you change (swap out) an computer, the other computers on the truck (including the dash panel's computer) all "learn" the highest hour meter reading the instant you power up, so swapping an ecu from an old truck will advance the hour meter in the new truck to match that older truck.