The only stuff on a car that you are not allowed to remove are safety decals such as CNG or electric/hybrid badges. The car must be clearly marked for rescue and service personnel. Don't want to accidentally kill any firefighters after an accident. (This used to be a big problem because hybrids have high voltage)
Other than that any signage can be changed to whatever.
A quality foam double stick tape will do you. You will probably end up covering the back of letters with it and then trim it with a sharp razor blade around the letters.
3M makes some awesome stuff called Adhesive Primer that if applied to the car and letters before the tape will make it hold so much better. I've installed lots of ground effects (factory accesory) this way.