Can the graphics processing unit (GPU) be disabled on a 2011 Macbook Air as a means of increasing battery life?
There is actually no dedicated GPU in the macbook air. There isn't enough room to house it. The only graphics you are using is the integrated graphics from your CPU. So if you were to disable it, nothing would display on the screen.
If you want to save on battery life, turn off your wifi when you don't need it, plus peripherals (backlit keyboard, dim display, unplug any uneeded USB's, etc.)