Write Entires with Fords?

Are we able to do a write entire on a 08 Ford Mustang and then change the vin number to match the vehicle? The problem I'm having is a customer bought a vehicle that will not pass PA Emissions because of the tune that was already done to the vehicle. I was going to play with a few variables so that he could at least pass as well as add Catalytic Converters back on to the vehicle. However, the vehicle keeps giving a invalid checksum error. I went to the local dealership to get the PCM reflashed to factory but they are unable to do so. This leads to my question. Can we do a write entire if we have a stock 08 Mustang file and I work off that file while making sure his VIN is still accurate for the vehicle?