My understanding is that state governors have roughly unilateral power to pardon state crimes. (First of all, is this true?)
If so, suppose that a governor were to announce something like the following: "For anyone convicted of a drug offense, I will give them a pardon halfway through their sentence, but only if their birthdate is on an odd-numbered day of the month." Effectively, this would divide the state's population into two groups of people that are roughly equivalent, with the exception that one group expects to face longer sentences for drug offenses than the other group. This would allow the governor to test e.g. the deterrent effect of longer sentences, or the effect of longer sentences on future recidivism.
Would there be any barrier to a governor using their pardon power in this way? Has anything like this been done, or seriously proposed?