This is a bit on the wordy side, (sorry), but I feel it’s important to the discussion.
I think what Marc is saying is that it is much easier to add the intonations by using local frame chains and not Master chain frames. You can achieve that by drawing in frames directly on the page where you want them, and not using the Master Page Editor to do this. You do not need multiple Master Pages, just the First and the Default. I like to think of the Master Page and Master Page Frames as the layout for the main composition material, and add in music frames locally (on the page itself - not using the Master Page Editor) for all the extra source music, intonations, prefatory stuff, etc.
Perhaps it can be done all with Master Pages, but it seems to add complexity. Remember that you can’t specify flows or players using a Master Page Frame Chain unless it is done in the Master Page Editor (which restricts things a bit when you come to pages that are different). Therefore, the real power lies in using local frame chains where the page is different because you can specify flows and players for each frame.
If your goal is to have a consistent or same look for the pages with the prefatory material, this could be easily achieved by copying the frames to another page to get a duplicate of any frames at the exact same position on another page. This is done by going to Engrave Mode, turning on Frame editing, selecting the desired frames, right-clicking on the page you want to copy to (upper left under Pages – the page will get a blue border showing it is selected), then select “Copy Selected Frames to Selected Pages”. After this operation, you will see your frame(s) duplicated on the indicated page, with their exact relative positioning, but with the original source material showing. (By default, Dorico retains the source material when duplicating frames, and you need to undo this default behavior.) The next important step is to click the Frame Chain dropdown and choose “Unlink”. Then you can specify a new flow and/or players for this duplicated frame! (Pretty cool, not well documented, and much easier to do than it appears in these instructions). This way of “duplicating” the look of pages is similar to using a Master Page layout approach, with the enhancement and freedom of specifying flows and players that are changing over the course of the project. Of course, at any page, you can always draw in frames wherever you want, but copying frames and their exact positioning is sometimes exactly what is desired.
An alternate way of achieving consistency is by using the same margin offest numbers (rather than trying to use a Master Page). This allows you to just draw in your frames manually and adjust them exactly as another page by putting in the same offsets. I personally find this approach cumbersome, involving jotting down all the numbers on a piece of paper and then going in and typing in the same margin information using the Property Panel.
You may find the following post helpful, as I give a simple example of Master Page frame chains and Local frame chains. In this example, my prefatory material is text only, but could have easily been music frames using flows of music snippets, which is the design you are looking for. The concept is the same: