Jawrgy,
Just take it easy and you wont get pulled over. I bought a gtr before I got my licence, had jap black tint on the rear windows so you could'nt see the rear P plate. Keep your front P plate in your door trim and if you do happen to get pulled over slip it up as you pull over. When they realise you are a P plater they will tell you you dont have your rear plate up. Let them know its there. Once they have seen it they will advise you to keep it on the outside of your window. Its happened to me a dozen times in the 3 year period.
This is not to say that when you do get pulled over you wont get fined for driving an over powered vehicle, 125 kw p/t. If they cant see the that green or red sqaure on your window they rarely look twice.