There is very little about the terms of a Decree of Divorce that is cast in stone and permanent. Except for the Divorce itself….but only after 30 days from signing. During that 30 day period after a decree is signed by the judge, either party to a final decree can file a Motion for New Trial if they believe they have been misled, cheated or defrauded.
But the other terms of a typical divorce decree, ie. child support, conservatorship, visitation, geographical restrictions can be modified as life conditions change, subject to some frequency restrictions under the Texas Family Code. In other words, you can't ask for a child support increase every time your ex's hourly pay rate goes up or down a few cents.
In real life though, people change jobs, careers, get raises, get laid off, decide the other parent isn't doing a good job, or alcohol and drugs cause a party to become a danger to the children. Remember that in many cases, people get a divorce while the children are infants or toddlers. This means that your divorce terms will be in place for 15, 16, or more years. In our mobile society, its not unusual for a parent to move, change jobs, or get a pay raise or cut many times over those years.
When there is a change in circumstances that warrants a modification of the decree, the court and a competent lawyer can help you make appropriate modifications to your decree.