From my little bit of experience with PA Soft all you will need to do is install the new clocks and change the mileage and then VIN in PA Soft. Get the mileage from PA Soft first, it will be in KM. Mileage checks are done every 100km so it should update eventually anyway. If the clocks have a higher mileage than the EWS and LCM they will update to the higher mileage. Not what you want.
To change the mileage down i think you have to wipe/replace the EEPROM in the clocks, this is age dependent though as early clocks could be changed down (possibly)