Ex signed and AGREED to ALL divorce papers including the proposed parenting plan. ALL the papers have been filed and a court date to finalize everything has been set, but he recently changed his mind about the parenting plan, now that he has his first gf since we separated. Can he file his own parenting plan, even though he's already agreed to one, if the judge hasn't signed the final order yet?

So the uncontested has now turned into contested and he will have to inform the court that he does not agree. The problem for him is that he is going to have a difficult time explaining the a judge why he has a sudden change of mind. Were you both represented by counsel? What is it he wants now?