(a) The court shall modify a parenting plan in accordance with a parenting agreement, unless it finds that the agreement is not knowing and voluntary or that it would be harmful to the child.
(b) The court may modify any provisions of the parenting plan without the showing of the changed circumstances required by 48-9-401(a) of this code if the modification is in the childs best interests, and the modification:
(1) Reflects the de facto arrangements under which the child has been receiving care from the petitioner, without objection, in substantial deviation from the parenting plan, for the preceding six months before the petition for modification is filed, provided the arrangement is not the result of a parents acquiescence resulting from the other parents domestic abuse;