Oh, so if you kill someone and we pass a law to make murder legal, then it's OK?
Is it OK to kill someone as long as it doesn't constitute "murder"? Is it OK for a woman's family in Saudi Arabia to kill her if she commits adultery? Is it OK for a soldier to kill an enemy in war? Is it OK for a man to kill another man who is raping his daughter? Is it still OK if the rapist has already finished? Is it OK for vigilantes to kill immigrants wading across the Rio Grande?
I don't need the law to tell me when killing is "OK" or not "OK"
But to answer your question, pardons by Governors and Presidents are common. A pardon is more than amnesty. A pardon says "you're forgiven"; an amnesty simply says we aren't going to put you in prison.