That depends on the year of your car. If your cluster looks like the ones in this thread, you would be able to do it. I think the display is estimated miles to empty by default. FWIW, I didn't think the MPG display was terribly useful; it displays a running average, not real time data.

If you're looking to have the outside temp display, make sure your car is wired for the sensor; I don't think the sedans are.