I don't think there is any way to change VIN numbers after it's been produced because if you look in the engine bay behind the engine the VIN number is etched into the body (maybe the engine block too??)...now I'm no genius but if they produced an '05 with an '05 VIN it would be kind of hard to change that VIN that's etched in there unless they sanded it down completely and repainted it.

I'm guessing it's a legit '06.