Is there a way of applying two master pages in one page?
I want to make an adjustable InDesign template for a report that could be used for various projects. So I want to have one of the master pages applied to all the pages of the report and the second master page to be applied again in all the pages but I want to have the ability to override only the items of the second master page.
No, multiple masters cannot be applied to a single page. Conceptually, master pages are alternate templates — an actual page in your document can only use 1 template at a time.
Now, you can do multiple master pages where subsequent master pages add to earlier master pages.
So, let's say you start with A-master. You can setup your basic page grid, etc. there. Then you add B-Master. When you create B-master you can choose for it to use A-master as its starting point. So the grid, etc. you have setup on A will show up in B. But you can then add more things, page numbers or graphics or a header to B without changing A. Changes you make to A will show up in B.
In this example, A-Basic Page Grid contains the rows, columns, and other guides that B,C, & D all are built on top of (see how they have the "A" over their pages, that means they are referencing A-Basic Page Grid).
Here you can see how B is based on A — Based on Master "A-Basic Page Grid"
These can continue to have parent/child relationships, so master C could be based on B, and thus be the grand-child of A... make sense?
If I understand your question, I think conceptually this should allow you to do what you want to.
The simplest way to work is to create a separate Master Page for each different in-document page appearance. Even if there is only a small difference between one set of Master Pages and another, this is the most straightforward way to have slightly different layouts within your document. [1]
Simply create your primary Master Pages. Then highlight those Masters in the "Pages" window, right click on them, and choose "Duplicate Master Pages" in the drop down menu that appears.
From there, edit your new Master Pages. Drag and drop them onto the in-document pages you want slightly different.
