I tried reading some fan-fics of HP , BUT they were mostly with using time-turners to change the past, or radical changes in the characters. (What if Harry had Voldemort's personality ? What if Harry was a murderous Juvenile Delinquent ? Some joes sent back in time and became somebody else ...). In one, Harry killed Uncle Vernon, Snape,Slughorn, and even Dumbledore (people who were either a threat or no longer of any use).
The Harry Potter fan-fics over at FanFiction.net are incredible in number.