How can someone already serving a sentence get a violent felony override?

Someone I know was persuaded by their lawyer to sign a plea deal for criminal possession of a weapon 2nd. He was informed by the lawyer if he signed the deal, the judge would classify his charge as non violent. Upon signing the deal and beginning his sentence, he was informed the judge did not classify the charge as the lawyer informed he would so the counselor informed the inmate his charge was classsified as violent.. Now he is unable to participate in certain programs that grants early release and the case is closed. The lawyer is not being helpful in any way but the only reason he signed the deal was because he was informed otherwise.