You can create a master variation that is based on and updates with another master (called the parent master) within the same document. The master spreads based on the parent master are called child masters. For example, if your document has ten chapters that use master spreads that vary only slightly, base all of them on a master spread that contains the layout and objects common to all ten. This way, a change to the basic design requires editing just the parent master instead of editing all ten separately. Vary the formatting on your child masters. You can override parent master items on a child master to create variations on a master, just as you can override master items on document pages. This is a powerful way to keep a consistent yet varied design up to date.

Original parent and child masters (left); when the parent master is modified, the child masters are automatically updated (right)