All I say is watch out. If you do this and have an accident and they notice this........ well you can figure out the rest. Obviously a fender bender wouldn't lead to a full accident investigation etc, but if you end up with a fatality or serious injury to the other party it won't help your situation that you have a modded GPS system that can also play movies.
I would love to do this in my other vehicle (no nav in the 4Runner) but have refrained solely from the point of what if I am in an accident. I wouldn't use the movie function when driving, but if I unlock that would be available and that is not a good thing