how can I enter a destination while the vehicle is moving

It's like texting and driving! ... Stop the vehicle to make the change!... No override!

Actually, for my 2004 and probably other years, there is an override. I agree with not doing this if you are a driver, but that's often not the case on long trips. Especially, family road trips, and this is why we even own something like this. Anyway, for the 2004, via the navigation panel, touch volume. Then touch the top left and then the bottom left corner of the panel (twice). Now hold in the "override" button until it is grayed out. Now click "back". You are now free to use all the functions. You'll need to repeat this everytime you turn off the car, but it's really easy.