I think you may be making this more difficult than it needs to be.
Putting Scrivener aside for a moment, what is the structure that you ultimately want in your document? The names of things are just words. That is, Scrivener doesn’t care whether you call your top level division a “Part” or a “Scene” or a “Flightless Bird.”
By default, Scrivener will use the structure you define in the Binder. Each document title will get whatever formatting you assign to that document’s hierarchical level. In Scrivener you can call that formatting “Heading 1,” “Heading 2,” etc., but you can also call it “Part Title,” “Chapter Title,” “Scene Title.” Again, those are just words. Scrivener doesn’t care, but since you ultimately want to manipulate the output document in another program, it will be easier if you use a vocabulary that is shared with that other program.
Now, Styles are the mechanism that you use to create that shared vocabulary. If a chunk of text in Scrivener has the Heading 1 style assigned, then another application that understands heading styles can use that information to preserve the structure you created.
In other words, assign Styles to the text that you want to be recognized when you re-split the document to bring it back into Scrivener. That will probably be the document names that appear in the Binder, and probably you will want your top level division’s title to be formatted with the Heading 1 style, the second-level’s title to be formatted with Heading 2, and so on.
To apply those styles via the Compile command, format the “title” text (line A in your screenshot) for the appropriate Section Layouts.
Does that help?