Intel HD4000 doesnt have any drivers, dont need to worry about it.
Nothing will happen to the OS, it will just register that there is new hardware and prompt you to get drivers for it.
You may have to re-configure display settings through Nvidia's tool, but it should stay generaly the same.
That happens when you change motherboards, or move the installation to a new system. Changing the graphics wont have that effect.
I'm relived now