I think the OP is asking how to swap a VIEW without changing viewCONTROLLERs. Am I misunderstanding his question?
In pseudocode, he wants to do:
let myController = instantiate(someParentController)
let view1 = Bundle.main.loadNib(....) as... blah
myController.setThisViewTo( view1 )
let view2 = Bundle.main.loadNib(....) as... blah
myController.setThisViewTo( view2 )
Am I getting his question wrong?