One key to being a successful parent after divorce is to clearly and directly follow the law. It is never a good idea to sneak around or do anything that a court would consider illegal. Sneaky, underhanded actions can result in penalties for the parent, ranging from fines to losing custody. In an effort to understand how to act transparently, consider a post-divorce scenario where the court order (typically the Judgment) provides that the son will live with mom. He is, however, actually living with his father, even though father does not have court-ordered custody. In this case, the father is technically in violation of the divorce judgment; the new arrangement is, after all, not what the judge ordered. Even if Mom approves of the child living with Dad, the situation still lacks a judicial "stamp of approval."
If there's one thing to keep in mind during divorce settlements, it's that much of the process is open to negotiation. As long as you continue to legally and responsibly advocate for yourself, there is a good chance that you will make gains toward more a favorable settlement.