Tex. Local Government Code § 262.031

(a) If it becomes necessary to make changes in plans, specifications, or proposals after a contract is made or if it becomes necessary to increase or decrease the quantity of items purchased, the commissioners court may make the changes. However, the total contract price may not be increased unless the cost of the change can be paid from available funds.

(b) If a change order involves an increase or decrease in cost of $50,000 or less, the commissioners court may grant general authority to an employee to approve the change orders. However, the original contract price may not be increased by more than 25 percent unless the change order is necessary to comply with a federal or state statute, rule, regulation, or judicial decision enacted, adopted, or rendered after the contract was made. The original contract price may not be decreased by 18 percent or more without the consent of the contractor.