Opie has the right idea. It's not so simple as swaping VIN plates. The VIN is also stamped into the frame of a car. If you have an accident and your insurance company finds out your car has different VINs, they won't cover you. This includes liability if you hit/kill someone else and get sued for $$$. You will be personally liable. NOT worth it. But if you strip a US car to the frame and build it up with WRX parts, legally it's a modified US car, but a US car all the same. The frame is the single irreducible piece of a car. You can swap the engine, drivetrain, interior, but the frame is the DNA of the car. Insurance should be okay; I'd check to make sure tho.
Good luck and keep us posted on your progress.