I had a left over civic cluster and changed the mileage to 0, and put it back together successfully. But there are pieces that are melted into place and not removeable by standard tools, you have to cut them out and re-melt them back into place. Of course, I tossed that cluster in the trash after I was done becase 1: Its illegal, and 2: The cluster had no tach, so it was worthless anyway. I was just seeing if I could do it.
But for an odometer that is going into an actual car, just leave it and write "exempt" on the title under mileage.. Or whatever your state requires for such things. If the cluster is higher mileage, snap a pic of the old one, then the new one, and save it to proove to your future buyer that the mileage really is lower than stated.