A personality rewrite was performed by the Hill Valley Police Department in 2035. Together with a sage implant, which alters the connection that connects a brain to the internet, its purpose is to rehabilitate criminals.
Griff Tannen was given a sage implant and a personality rewrite, and was allowed to join the police force afterward. However, they didn't do much to curb his aggressive and criminal tendencies, as he received multiple warnings for taking bribes and using excessive force.
After Marty McFly and Emmett Brown crashed through the Lone Pine Fli-Drome, they were deemed terrorists. Doc Brown was able to get to 2015 via the temporal field generator Mk II in his secret lab. However, he had to leave Marty behind, since he only had one diving suit, which was needed for protection against the rigors and temperature variation of the space-time continuum.
Marty was going to be given the same sage implant and personality rewrite that Griff had received, but Doc had managed to convert a second DeLorean into a time machine, using a Mr. Fusion from 2015, and the flux capacitor and time circuits that he built for his steam time car in 1893.