If, for example, Schwarzenegger commutes Tookie William’s death sentence to life without parole, can a future governor or other entity re-instate the death sentence?
About five years ago, Illinois Gov. George Ryan commutted the sentences of every prisoner on the state’s death row. His successor (Rod Blagojevich) tried to see if there was anything he could do about that - he felt Ryan had overstepped his authority by offering blanket clemency to 167 prisoners. But Ryan’s move stood. I doubt a Governor has the power to reinstate a death sentence; ditto for sending a pardoned man back to jail. It sounds like that would violate double jeopardy, if nothing else.
Re governors freeing people, is there a legal distinction between commuting a sentence and pardoning someone?
Commuting a sentence changes the punishment handed down into a different one that is viewed to be less severe. For example, the death penalty is changed to life imprisonment.
A Pardon removes any penalties associated with the crime (jail time, fines, etc)
A pardon is like a legal reset button. It clears the legal slate, making it as if the conviction never happened (or, if the pardon is issued before conviction, forecloses prosecution and conviction). I don’t think, if one is fined upon conviction, that one gets a refund if one is later pardoned.