When you insert a citation, Cite While You Write takes action:
It formats each in-text citation according to the selected bibliographic style.
It adds a complete bibliography to the document (unless you override this with a setting in the output style).
As you add citations to your paper, the bibliography is automatically updated with the rules of the current output style.
To reformat your paper in a different style:
In Pages, go to the Edit menu and select EndNote Citations, then Bibliography Format, and then select an output style from the available list.
Your citations and bibliography are updated for the new bibliographic style.
The styles that are available in Pages are the styles marked as “favorites” in EndNote. See Adding Styles to the Output Styles Menu for information about expanding the list of available styles. If you add more favorite styles to the list, you need to close and restart both EndNote and Pages in order to make the styles available in Pages.