I find intuitive to try to collapse large notes aswell with the same button as nested-lists. The expandable-on-inside-click is ok, but is annoying when writing some maths, links and code snippets that are shown when leaving the notes-area, then you are forced to set full-view for the entire document, instead of the sections where one is activelly working.
Maybe I need more coffee, but I failed to comprehend what you described.
Something about the 1-line notes option in settings?
And you want to customize the appearance with custom CSS perhaps?
It just clicked. You want that setting to toggle that setting on just one note, so you can view rendered markdown quickly while editing. Makes sense.