What you’re looking to do cannot be does easily. If I understand correctly, what you want to do is to somehow automatically add a field when editing an ACF field groups.
Instead of building a new setting for an existing field to do what you want you might want to look into building a new type of field https://www.advancedcustomfields.com/resources/creating-a-new-field-type/. Doing this would let you add all your own settings and build the JS needed to make it work.
