In order for any court to have jurisdiction to enter an order in a child custody matter, the child must have lived in that state for the past six months. (There may be situations where the child has not lived in any state for the past six months and no state fits that description, but that is another issue for another day.) So, what happens when you need to modify an old order from another state?
Once the child has lived primarily in Texas for at least six months, you can bring a suit to modify a foreign order in Texas. If there is any dispute about where the case should be heard, the original court (known as the court of continuing jurisdiction) must make a determination as to the proper court. If both parties agree that the child has lived in Texas for at least six months, they can move forward with the case in Texas without any need to involve the prior court.