Fraud or misrepresentation: If one party engages in fraud or misrepresentation during the divorce proceedings, this is grounds for modification. This can include concealing assets, providing false information, or deceiving the court or the other party.
A divorce decree could be invalid if a judge's decisions were based on incorrect information or if the judge made errors affecting the outcome. If one party concealed assets or debts from the other, that could be grounds for appeal or modification.
In the US you generally don't need consent to get a divorce. If one person refuses to cooperate, the judge will order them to. If they still refuse, the judge could find them in contempt, or they could order the divorce granted based on the information provided by the plaintiff.
Yes, you can amend a marital settlement, with both parties agreeing.
If a divorce decree has been issued, you can only contest it in extraordinary circumstances. You can still try to contest the term of the divorce, but you would face an uphill battle since you already agreed to them.
To modify alimony there must be a material (important) and substantial (major) change in circumstances since the divorce that not expressly stated in the divorce decree or in the findings that the court entered at the time of the divorce decree.
When a person is not following the divorce decree, a motion for contempt should be filed with the court that ordered your divorce. You would file the motion for contempt and have a copy served on your ex spouse. The judge will schedule a hearing and determine what is going on in this situation and may issue fines, etc.
It cannot be waived, no. The court can enter a judgment making the marriage automatically terminate once the 90 days is up, but the 90 days must pass before the marriage dissolves. There is no way to sugar coat that.
Parenting time and child support, which are also part of a final decree, may also be modifiable. At the time a divorce is finalized by court order, so are visitation and custody agreements.