Motions to Vacate
A motion to vacate asks the court to make a previous order void. In some jurisdictions, a motion to vacate is also called a "motion to set aside" as that is literally what the motion asks the court to do: set aside the previous order and make a new decision as if the order never existed. These motions are used when the party who wants the previous order set aside does not have the right to appeal the order. If the court denies the motion to vacate, the party has the right to appeal the order of denial, but not the original order she sought to have vacated.
If one of the parties fails to timely file an answer to a petition for divorce or attend a final hearing on the divorce, the court might issue a default judgment against that party. Normally, this order grants the requests of the other party and it can include an order of custody. The party in default cannot appeal a default judgment; he must ask the court to vacate the order granting a default judgment. The grounds for vacating a default order vary from state to state, but generally the person requesting it must prove that his default was excusable, inadvertent, mistaken or that he has a meritorious claim that the court should consider; for example, a reason that the default was excusable might be that the party was not properly served with notice of the proceedings.
If the parties agree to a custody order, neither party can appeal it. If circumstances have changed since the court made the order, you can file a motion to modify the order. However, if the circumstances have not changed, a motion to modify is not appropriate and the court will not grant it if filed. If the agreement was induced by fraud or made under duress or undue influence, you can file a motion to vacate the agreed order. As legal terms can have slightly different meanings and interpretations in different states, you should consult with an attorney in your state to determine how to proceed.
Ex Parte Orders
If one of the parties gets a custody order from the court without giving the other party the opportunity to be heard, it is an ex parte order. Normally, these are temporary orders and the court will issue the order and schedule a hearing on it. Since the other party will have the opportunity to be heard later, a motion to vacate is not normally necessary. However, in some cases, one party might allege to the court that an emergency exists, such as child endangerment, and that the court should issue an immediate order that is different than a previous order. The other party can file a motion to vacate stating that no valid emergency existed and ask the court to set aside the ex parte order instead of holding a hearing on it.