As capsat asked; and you are in Lahore, kindly visit Excise office for details and share with all at Pakwheels. If you decide to visit, kindly ask them about any impact on the annual token fee after new registration. I believe there should be no WHT (Withholding tax) on older cars with new / revised registration. The first date of registration remains valid...right? Also get details about total expense for re-registration according to engine power c.c's.
Your effort will be a great help to all concerned. Jazak Allah Khair.