What is the best way to reestablish the custody schedule after being too friendly with the situation?

Well, you do not indicate how long the reality has been any different than what the decree says.  There is a case called Rivero that indicates that if there is a court case, what the parties have actually been doing for the past year will determine the legal label applied to their conduct.  For details, see http://willicklawgroup.com/child-custody-and-visitation/. Generally, however, if what you want to do is exercise custody and visitation precisely as the order indicates, the reasonable thing to do would be to give notice in writing that such is your expectation beginning on a certain date, and then begin acting in accordance with the existing order.  Anyone unhappy with that arrangement would have the burden of going back to court to change it.