I have a document that has multple master pages — 74 of them, to be exact. I need to change the left and right margins to an identical measure for all. However, I don't see a global way to do it. Is there?
Did you try File>Document Setup and then change the margins?
Of course. But the effect is not across the board. In fact, only one master page change; it did not apply to the rest. I figure this must be because those master pages were configured individually, so File > Document Setup doesn't apply to them. Thanks for that tip. I remain open to a solution.
To change the margins on multple master pages in one go you need to have them selected in the Pages panel.
Under the Layout menu go to Margins and Columns....
You'll need to ener each Margin (Top, Bottom, Left and Right) in your case the Left and Right separately.
NOTE: Before selecting the master pages and doing this step make sure the chain link is disabled.