As you can see below, trying to add text to the menu is impossible since we cannot link the text to open up the menu page.
Do you want to show lightbox? Or something else?
Apart from opening a user made lightbox menu as already mentioned another way around this might be to make a horizontal menu with a set width small enough to show just the MORE option and change it to say MENU instead of MORE. Thus when the MORE/MENU is activated you’ll see the other menu items as if they’re a submenu dropdown. This might be fiddly to get working on all screen sizes but something like that is doable and might be close to what you want if you don’t want to go the lightbox route (which is certainly the best way to achieve a fully customisable menu for sure)!
Example of how it looks “closed”:
And “open”:
