With digital/electronic speedos it is easy, you can choose in the ecu programme to show mileage kilometers on the trip/odometer - the speed is ususally shown in both. With the older ‘clockwork’ types you can either change the fascia of the speedo or use stick ons - but you can’t change the mileage and trip readings - the only way to do this is to replace the speedo head with the appropriate type.
With the digital ones, even if the mileage reading has been ‘corrected’ the ECU stores the total time and speed the vehicle has been driven and you can cross check within around 5% accuracy the total distance the vehicle - (or at least the ECU) has done independantly of the display reading…
