I look at this question and wonder, "What have I done... Ever?" It's hard to come up with anything most of the time, even looking back, my class would have never had "that one kid that can't play sports and sits around on some tech 24/7" but who needs that anyway. My family would have been practically the same except for my parents becoming alone 4 years sooner. Heck, Pokecommunity would be extremely the same without me, I'm sure, I'm not making new rules or anything. XD
But then I realize, there's one person that I've changed. My first friend in Kindergarten and I was his first true friend it seems. He never opened up to people but we shared a common interest and with that I was able to help him become more social, or I tried anyway, and since then he has opened up to more people and has been able to move on when he had to move away...
So, even if it's only one life... I'm glad I was there.