Impermissibility of changing one's mind after the judge has ruled and the victim has agreed
a judge gives a verdict according to Allah's Purified Shar` (Law), all parties must abide by it. If a claimant waives his right, it is not permissible for him to ask for this right at a later time. It is worth mentioning that whoever waives his right with the intention of attacking his opposing party later is a sinful person who is committing a major sin and deserves punishment. Allah (Exalted be He) says:
But if the killer is forgiven by the brother (or the relatives, etc.) of the killed against blood-money, then adhering to it with fairness and payment of the blood-money to the heir should be made in fairness. This is an alleviation and a mercy from your Lord. So after this whoever transgresses the limits (i.e. kills the killer after taking the blood-money), he shall have a painful torment.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.