Child support, primary custody and visitation can be changed later. Texas law says these things can be changed if there is a material change in circumstances of the child or party. Material means important or substantial.
For child support, a party could lower child support if they can prove they make less money, and it is not their fault. You may also increase the amount someone owes in child support if they have begun to make more money.
For custody, an order can be modified to protect the safety of a child. Visitation can be changed to help a parent see their child more often. A parent may even want to decrease their visitation because of work. In some cases, it is better to have a visitation order reflect what you can actually do. To not exercise visitation that you have a right to can reflect poorly in later litigation.