No, not a change.
And 2A for just sensors! Are those sensors heaters?
And 1A for the onboard regulator, not a change in heaven it can handle 1A. If fed by 12V it can handle the Mega + a hand full of led's and it's done.
You can use a 5V supply. Just connect it to the 5V pin of the Arduino and connect the sensors directly to the supply as well. One note, if the Arduino is powered from an external 5V, DON'T connect the USB.