Knew a guy who was sentenced by a judge to be a “trustee” at a prison, he was quick to point out he was never a (normal) inmate, trustees work within the prison, not as guards, for no pay - they do things that some non-inmate employees get paid to do. Depending on the situation, it might be a small transition from guard to trustee - but I highly suspect that whatever the guard did to be incarcerated would best be handled with him as an inmate (which trustees technically are) at a different prison.