I'm guessing the warning is like a "Don't pay too much attention to the screen while driving" kinda thing?
I don't think it's much of a big deal since all cars with navigation systems do this same thing (from my experience). My parents' Mercedes both require you to hit the "OK" button when you wanna access the navigation. My brother's RX300 requires you to press the "I AGREE" button on the screen (it's a touch screen) every time you start up the car, and with my car, whenever I pop up the navigation for the first time after the car has been started, I have to press the joystick button to say "I agree" to whatever the hell the warning states before I can start using the navigation unit.
Not only that, Japanese cars (both my Infiniti and my brother's Lexus) don't allow you to input a destination in the navigation while the vehicle is moving !! How stupid is that??
My point is that there is probably no way to override the warning, but all cars with navigation systems (or iDrive) have this initial warning every time you start the car.