Parents frequently work out arrangements between themselves, such as a schedule change, a new pickup location, or an adjustment to a holiday rotation, without going back to court every time. Those informal agreements can work well for years, and they can also become a serious problem the moment one side needs the other to actually follow them.
The gap between an agreement and an order
An agreement two parents reach on their own, whether in writing, by text message, or verbally, is a private arrangement between them. A court order is a directive from the court that carries the court's enforcement power behind it, including contempt proceedings in some jurisdictions if it is violated. A private agreement that was never submitted to and adopted by the court generally does not carry that same enforcement power, no matter how clearly it was written down or how long both sides have followed it.
Why courts generally require this distinction
Courts that oversee custody and parenting matters typically retain ongoing authority over a child's welfare for as long as the case remains open, which is part of why an agreement between parents is usually treated as a proposal for the court to adopt rather than as a self-executing contract. Once incorporated into an order, the terms carry the court's authority; before that, they generally carry only the parents' good faith.
What tends to happen when there is no order behind an agreement
If one parent stops following an informal arrangement, such as reverting to an old schedule, making a decision the other parent thought required joint agreement, or simply disputing what was agreed to in the first place, the parent relying on the informal agreement may find there is little the court can immediately do, because there is no order to enforce. What existed on paper or in a text thread may still be useful as evidence of what the parties intended, but it is a different, weaker position than having the same terms in an actual order.
Where this fits into a case
Whether a particular informal agreement should be formalized, and what process that requires in a specific jurisdiction, from a simple stipulation to a full modification proceeding, is a question a licensed family law attorney can address directly.