If you decide to drive a different car to the airport, then it's not an issue. Here you will find information regarding shuttle and valet parking.
You can easily change the number plate in your confirmation email via manage my booking. Did you not have to submit a number plate at the time of booking? Then there is nothing to be changed and you can drive straight to the parking place.
With valet parking, it is important that you inform us of the change in vehicle, as the driver will be looking out for your car at the departures hall of the airport. You can also call the parking provider to inform them of the change of car.