Banned? No car is 'banned'
But yeah as far as the engineering aspect of the car goes, it's got quite a lot of restrictions when it comes to the ECU. It's got a top speed limiter at 112mph (170kph) and that can't be turned off unless you buy your car in the United States- there's no limiter for the USDM models.
As far as modifications go, no GT-R35 has been modified yet that I know of. I don't think there's a piggy back or even a software upgrade that disables the top speed limiter out in the market... yet.