Reordering Custom Master Pages
Custom master pages appear in the order created while in master page view. Now, you can change the order at any time for added convenience while in master page view:
Switch to master pages (choose View, Master Pages).
Select Format, Page Layout, Reorder Custom Master Pages. The Reorder Custom Master Pages window appears, containing a list of all custom master pages in the current document.
Click on a master page name in the list; then click the move up or move down button (Figure 2).
Figure 2 You can change the order of custom master pages.
Click the Set button to change the order.
You cannot change the order of Left or Right; they always appear first in master page view.