Generally, unpaid restitution becomes a civil collection issue. In order to do what you are proposing, you would have to put your case on calendar, have a rehearing on the restitution amount, and get the Judge to order a lower amount. The difficulty is that the Defendant's ability to repay is not the standard that the Court uses, rather, the standard is what are the losses due to Defendant's conduct. I agree that you should speak to an attorney to see what he or she thinks. Good luck.