How does the EV mod affect your mileage?

That's where I say "sometimes yeah sometimes no."

If there's little/no chance for battery regen, you will most likely kill your mileage if done time after time. If it's the random stoplight/four-way stop in the middle of nowhere with tons of regen opportunity before and after the stop then go for it. But it's not like you can stomp on the pedal and squeal the tires in EV. It's still a steady and relatively slow acceleration.

The absolute worse that can happen is that the battery will deplete faster than expected and the mileage will drop. Both of your arms will most likely still be attached, the sun will not burn out any faster and gravity will probably not be affected.