Can you have the sentence from a plea agreement changed or reduced?

The short answer is a qualified maybe (and that is a long shot). When a defendent accepts a plea, part of the agreement they sign is they are "waiving their right to an appeal". So on it's face, there can be no appeal - which is the only way to get the sentence changed. When the plea is presented, the prosecutor's offer is not always accepted by the judge. If you take a plea, you are at the mercy of the sentencing guidelines and the pre-sentence report - and the judge who is not bound to any the plea deal, only a sentencing recommendation. If the judge meant to go "concurrent" but mistakenly did "consecutive" you can petition the judge with the prosecutor who will agree with the error. That is the most likely chance the is for a change to this sentence