Responisibility of child

I was looking for any cases that you know of where:

I thought I read awhile back when there is joint custody and if a parent actually gives the responsibility of their child to the step parent, the responsibilities like the step parent goes to the parent teacher conferences, doctors appointments, dentist appointments, etc then the parent is shifting their parental responsibilities to the step parent. This would give the other parent the right to modify custody of the child.

Meaning: 2 parents with joint custody of a child, Parent A is remarried and Parent B is single. With Parent A having the step parent take care of the child, rear the child, take the child to practices, events, parent-teacher conferences, doctor appointments, dental appointments, parent A shifting their responsibilities to the Step Parent, actually creates a case for parent B to modify custody due to parent A passing their responsibilities to the step parent.

This question is outside of the scope of the forum. Without performing any legal research, I am unaware of a specific case that says that the shifting of duties to a step-parent is a substantial change in circumstances warranting a modification of child custody. You should consult with an attorney to explore the impact these changes have had on the child and whether that would be sufficient.