Dated receipt and engine details, plus the recorded mileage of the vehicle at each MOT would be enough to satisfy any future buyer that the engine has had less use than the odometer suggests. But the odometer is attached to the car, not the engine, so shouldn't be changed.
my odometer is on kmh and every year the mot man records it as miles.
dunno what will happen if one day the mot man records it as km or converts it to a mileage reading in miles :/
If I was buying it I'd far rather have the true mileage displayed, and would be more likely to believe you if you told me about the engine and showed me the paperwork than if you explained that you'd altered the recorded miles.