I assume you are referring to a rear door and not the liftgate. Check the available locking settings in the owner's manual, I think you'll find a setting that my accomplish your goal.
That's typical for new cars, and an obvious safety measure. My own conclusion was that it's more trouble to mess with it than it's worth. All I need to do to use it is to stop for a moment and trigger the lift gate to rise.My bad. I meant the liftgate. When the Murano is in drive gear, I can't open the liftgate.