Some years ago I did a sermon on Adam and Eve, mentioning that some scholars suggest that God acted with mercy in their case and let them live longer, rather than killing them immediately after their sin. I said that God never changed a punishment based on a specific commandment.
That assumes that when God threatens a punishment, repentance is often, if not explicity stated, then implied, such as in the preaching of Jonah to the people of Ninevah. He preached that God would destroy the city. They repented and God relented. The condition of repentance, however, was implicit in his preaching, and the prophet halfway expected it to happen, it would seem.
Having said that, is the statement above true, that God never changed, or relented on, a punishment based on a specific commandment? Somebody may quote Cain, but does that apply?