I agree with Attorney Priedkins, and the other attorney get it in writing and approved by the court.
Please only call me if your case is in California as I am only licensed here and laws of other states may vary. I approach trials and issues from a legal and common sense approach, This is how the majority of judges I have appeared before in 40 years also make decisions. I do not intend by my advice to enter an attorney client relationship and in most cases advise to obtain legal representation. Sometimes if you can not afford it a consultation or limited scope representation is available. As an experienced attorney I can tell you, judges can be impatient, hate emotional arguments and over exagerations or lies. A brief outline of the problems and desired solutions is always best and I often in limited scope representations advise clients on how to proceed at time of hearing or trial and my fees are considerably less when I do not appear in court as it takes much less of my time.
If both parties can agree, you are always free to amend your child custody/parenting plan agreement without entering anything in writing to the court. However, know that if either party disagrees with the changes it is their right to return to the original court order. If you want to protect each other from the ability to return to the original or current court order you should follow the advice of the previous responses and file a stipulation and order with the court.
You and your ex can do anything you want as long as both parties agree. The Court doesn't follow after you checking to make sure that you are doing what the order says. If the two of you are getting along, the Court is happy. However, there is a reason that the two of you are exs...you can't get along! There is always a chance that there will be a disagreement over the new arrangement at some point, and for this reason, its best to get everything in writing and signed by the judge so that it is enforceable should you have a falling out at a later date.
Sign up to receive a 3-part series of useful information and advice about child custody law.