ECM Replacement

[tresero]

I need to change the ECM and I notice on Rock Auto it says that

"vehicle specific Flash programming req'd ON or OFF the vehicle.Accurate VIN and mileage are req'd. Additional vehicle specific on-car programming must be performed AFTER installation to prevent drivability and starting issues."

I am confused if I can do this, or if I have to spend money on an EPROM programmer or something. It sounds like they do a general program when you buy it, but you need to tweak it?

I need to get this done to pass smog since it is showing a phantom check engine light.