(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 change circumstances required by subsection 9-401(a) if the modification is in the child's 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 parent's acquiescence resulting from the other parent's domestic abuse;
(2) Constitutes a minor modification in the plan; or
(3) Is necessary to accommodate the reasonable and firm preferences of a child who has attained the age of fourteen.
(c) Evidence of repeated filings of fraudulent reports of domestic violence or child abuse is admissible in a domestic relations action between the involved parties when the allocation of custodial responsibilities is in issue, and the fraudulent accusations may be a factor considered by the court in making the allocation of custodial responsibilities.