You have to pull the old one off the holder as it is stuck on. Then there are screws to come out. Unfortunately when you take it off there will most likely be scratches on your bumper.
Stick the new one on with number plate double sided sticky sponge and it save the bother of drilling etc.
Next is the legality, it is illegal to have an import plate on a non import car, so you can get pulled over for it, i have had number plate on for two years and i have been pulled over but nothing was mentioned about the plate.
Here is what postition mine is in.
I got some jap-sized plates made up, with the lettering in the correct font, as big as would fit, but they're still smaller than standard. I haven't been pulled for it yet, or even had anyone mention it (I have friends with family in the force).
The only questions the guy asked where "whats your reg?" and "do you want a border on it?"