My gateway is a serial gateway built with an easy newbie PCB and a pro mini.
What I did when I upgraded my 1.4 setup to 2.0, I pulled my pro mini that I had flashed with the 1.4 setup and put a new pro mini in that had 2.0. That way if there were any problems, I could easily swap the 1.4 pro mini back in to easily be back where I started.
Likewise when replacing your library, pull the MySensors folder out of your arduino libraries folder to keep as a backup until you know things will work. That way if you have to revert back, you can easily swap back the old MySensors folder. You have to completely remove it from the libraries folder though, you can't just rename it to something else.