This message was posted on behalf of Intel Corporation
The only way to access the USB pins is from the USB connector available on the Mini-breakout board. The USB pins are not connected to the header array, so you cannot access them this way.
Regarding the second question, you could add an extra button to one of the GPIOs in the header array, and execute the command "shutdown" when the button is pressed, but you will have to use the power button available on board to start the Edison again. Unfortunately, the push button available on board cannot be used without waiting for the 10 seconds.