There were some executive actions, so it can be reversed:
- Created the data driven justice initiative. This opened communication between forces in towns and cities with a focus on cutting unnecessary arrests and reducing pre-trial holdings.
- Clemency initiative (release non-violent prisoners with pardons).
- Established the President’s Task Force on 21st Century Policing. It focused on high impact reform and published reports. Obama made a few moves based on their reports such as removing the criminal history box from most federal contract positions.
- Estsblished the Federal Interagency Law Enforcement Equipment Working Group in response to Ferguson. It targeted acquisition and use of military grade equipment. Trump reversed all of their work.
- Spearheaded the justice department smart on crime initiative. It "increased focus on violent and serious crime, decreased prosecutions for low-level, non-violent offenses, seeing a 20% drop in charges."
- Revised the Edward Byrne Memorial Justice Assistance Grant. The justice dept removed some incentives to increase unnecessary incarceration on non-violent crime, including mandatory reporting on volume of arrests, amount of drugs seized, and the number of new drug-related cases opened.
- Signed an executive action to phase out private prisons, that's gone.
- Reduced the 100-to-1 sentencing disparity between crack and powder cocaine.
- Hosted round tables in response to Ferguson between law enforcement officials and activists like BLM.
There's lots of things I'm missing. He also wrote this article for Donald Trump and the Justice Department:
https://harvardlawreview.org/2017/01/the-presidents-role-in-advancing-criminal-justice-reform/
So far just lip service...but it took Obama a bit before he could really get at justice reform.