I did this quite a while ago, I'm not the best electronically minded but the instructions were helpful.
At one stage I think I had some of the wiring wrong and the car wouldn't start at all haha.
Anyway, I put a switch next to all the other switches to the lower right panel of the drivers seat which disengages the VSS.
You need this because when the VSS is on, the nav will function like normal and you won't be able to input destinations.
Once you flick the switch, the keyboard becomes enabled and you can type away, but the vehicle loses its position on the map because it thinks you're stationary.
When you've finished, flick the switch back over and it will take maybe around 10 seconds for the GPS to figure out your new position.
No other glitches.
The other thing that performs a little differently is when you press the phone button on your steering wheel while in motion, it won't go directly to the speed dial screen. It will instead go to the phone keypad screen and you will need to press "Speed Dial" on the screen, or dial a number.
Note: I only did this mod so my partner could put in the destination while I drive. Drive safe!