How do I import and replace parent pages?

Hello. I have several long Indesign files to eventually compile into a book. I altered margins, guides and running headers in the 'A' Main Body parent page of one of the files. I'd like to use that 'A' parent page across the rest of the files. I tried applying it to the other files, but it creates an extra  'E' parent page instead. I then tried a couple of things, including applying that 'E' parent page to all pages, but it places that information atop what's already there rather than replacing what's there. I also tried dragging 'E' on top of  'A' in the parent section of pages, and it does something similar. How do I import the parent page 'A' so that it simply replaces the current parent page 'A' and applies its settings to all 'A'-based pages?

Thank you