The court shall not modify a prior decree allocating parental rights and responsibilities for unless it finds, based on facts that have arisen since the prior decree or that were unknown to the court at the time of the prior decree, that a change has occurred in the circumstances of the child or his residential parent, and that the modification is necessary to serve the best interest of the child. In applying these standards, the court shall retain the residential parent designated by the prior decree or the prior shared parenting decree, unless a modification is in the best interest of the child and one of the following applies:
(i) The residential parent agrees to a change in the residential parent.
(ii) The child, with the consent of the residential parent, has been integrated into the family of the person seeking to become the residential parent.
(iii) The harm likely to be caused by a change of environment is outweighed by the advantages of the change of environment to the child.