I don’t think you will be able to recalibrate the ecu but you can interrupt the signal to the dash with a speedo healer and calibrate it how ever you like. They are really common on bikes when changing wheel size or sprockets. But they are not cheap.

ive just picked one up to play with this weekend if the weather stays dry. I’ve changed from an mtx75 to a Mt75 and it’s reading around 5mph at 60.