your allowed to change the millage , as long as your not trying to selling the vehicle and claiming its low millage ,when its not, also mot history can prove it , its fairly normally with cars that have HAD to have the clocks replaced due to a fault, and the new clocks may say 0miles, (thats if the memory is stored on the clocks or such)
it maybe worth taking the clocks out and pressing on the lcd, ive once done it on a k11 and simply put the it had a loose connection and pressing it made it work again
maybe worth a ask on the fb page? aswell for clocks with near the same millage