How can I legally stop paying child support if my son chooses to live with me?

You are spot on correct that you should do this by petition. Do not just stop paying. Instead, using the court rules, write a petition to advocate why your change of circumstance meets the legal requirements to get the judge to consider the new arrangement in place for the next school year. You have to give notice to the mother, former spouse. If she comes, she comes. If not, your request might go unopposed.

I agree with Mr. Brinkmeier's answer. The worst thing you could do is simply stop paying the child support without seeking a modification of the court order requiring you to pay child support. I would encourage you to timely file your petition to modify the court order to coincide with your son living with you again as the court will not have the power to retroactively go back to "revoke" a child support payment unless you have already filed your petition to modify and have served legal notice on your ex-wife. I do not encourage you to attempt to modify a court order without the help of a family lawyer. The Office of the Attorney General administers the Title IV-D Child Support program in Texas, and offers its services at no charge to those seeking assistance with child support, but the AG's office is a very busy place and probably isn't your best bet in this situation. Best of luck to you!

You are right. File a motion to modify the parent child relationship AFTER your son comes to stay with you. Do not stop paying until you get an order from the court. Your ex will have to come to a hearing if she wants to oppose your modification. If she does not show up, you will be entitled to a default judgment in your favor. Good luck!