The VIN plate (chassis number) will tell where a car originated from.
To bring a car to Greece (or any other EU country) for 6 months temporary import, you must have owned or been the registered keeper of the car for 6 months prior to bringing it here. When you are here with the car, only you or members of your immediate family, are legally entitled to drive the car.
Whether the car is right or left hand drive is totaly irrelevant.
Agree with what baywatcher says but I think if the car is over about 10 years old, then the tax starts to get higher again. (it would have no Certificate of Conformaty)