I think you are saying you want to switch between custom settings and change that display setting (as opposed to a setting that affects the recorded image). As far as I know, the display settings persist across all dial positions (PASMC..). The strategy I use is to assign custom settings to modes of using the camera, i.e. landscape, portrait, street, etc. if there are different things I like to do in those modes, I decide where to put modifiers, like face detection, film simulation, etc. You have 3 more choices: button, the Q menu, My Menu. If you need it instantly (face detection on/off, subject detection) I put it on a button. If I like to be able to see the state because I change it often, I put it in the Q menu. I only use 8 and it's the things I change the most. MyMenu is where I put the next level of things I change, including most things I change from default so I can verify they are set correctly.
tl;dr; Put it on a button if you change it frequently, or MyMenu.