This movie is based on the book "A Time to Kill" by John Grisham. I have read it. Acccording to the book, after the verdict is delivered, Jake (the lawyer) goes to meet one of the jury members. That woman was not at home but his husband was, who was on the grand jury which indicted Carl Lee Hailey. He told Jake that when they were all discussing the verdict in the chambers it was almost a tie. Then his wife told everyone to close their eyes and imagine a white girl getting raped by two black men. How would they deliver the verdict in that case? Everyone realized the severity of the crime committed against Tonya (Carl Lee Hailey's daughter who was raped) and thus declared Carl Lee Hailey not guilty.
According to the book, on the day before the verdict was delivered, the jury told Noose that they wanted one more day to deliver the final judgement because they felt intimidated by the Ku Klux Klan. They didn't give a judgement to Noose in the first place. There's no question of changing it.