Generally speaking, the courts prefer to keep things as stable as possible for children whose parents are divorced. Once a custody and visitation schedule is in place, it isn't supposed to be altered without a good reason.
So, what counts as a "good" reason to ask for a post-judgment modification of the custody plan? If you're unsure if your reason is good enough to go back to court, ask yourself the following questions:
1. Is your child's life being disrupted already?
What is the motivation for your desire to change the custody plan? What triggered the belief that the old agreement is no longer workable?
For example, is your co-parent trying to move more than 100 miles away from where you are now? Is your ex moving somewhere within that 100-mile radius, but the move will still make it impossible for you to continue with the same visitation schedule and remain as involved with your child's lives? Has your co-parent developed a problem that now makes it impossible for them to provide the right nurturing and care for your child due to poor health or some other reason?
2. Do you believe your child is in danger?
If your ex-spouse has developed a substance abuse problem, your child could very well be in danger due to neglect.
Mental health issues may also pose a problem for some parents. While you likely shouldn't try to ask for a change in custody simply because your co-parent suffers from depression or anxiety, it is appropriate to ask for a change if their condition causes them to neglect your child, requires frequent hospitalizations or involves psychosis.
3. Is your co-parent ignoring the current order or interfering with your relationship with your child?
Some parents will use their children as weapons to get revenge on an ex-spouse. If your ex-spouse routinely ignores the visitation schedule, withholds access to your child on a whim or seems to be "demonizing" you to your child to the point that your relationship with your child is becoming unnecessarily strained, that's a good reason to ask the court to take a new look at the situation.
If you've answered, "yes" to any of these questions, it may be time to seek advice from a family law attorney.