There are three points to this triangle of validation. Two of these points are fixed. First is the managed object class of the parent (which is fixed). The second is the name binding (which is also fixed). The third is the managed object class of the instance being registered (this is what you just tried to change from the original value). The new managed object class must allow the use of the original name binding to create a new instance of the new managed object class under an instance of the parents managed object class.