2-3. Perhaps I should have explained it further, by opening a 'generic menu' I literally mean a menu/file with class = &GenericMenu;. There are certain limitations that come with it, like inability to give elements any IDs (if doing so the menu will close when they are clicked, regardless of the actual ID used). The real 'strength' of a generic menu is that with this function you'd be able to open it from any menu or gamemode and have full control over which file is used. Apart from the class, almost anything can be added in the menu.
Could this be used when I want to open a menu for the player to choose some options? I don't mind if the menu automatically closes when a button is clicked (as that's how the normal generic menu works anyway), but would like to have the ability of aligning things differently, have images in it, etc. What I do need, is to be able to read which button was clicked (just like the normal menubox).
How OverrideXML works is by changing the filepath the game uses when a menu is opened. Currently it will remain that way for the remainder of the session, in time I hope to also allow one-time-use. It is mainly useful for when you have a mod that, depending on the cirumstances, changes how alchemy works (and for example, change the xml file to reflect it). Normally if you want to change the layout of a menu the best way is to change the actual file. But this means it is either yes or no, nothing in between. Now a modder can change this on-the-fly.
One use that came to mind, was Enhanced Economy's Auto Haggle feature. It opens a generic Barter display menu instead of the standard Haggle Menu, but EE also includes an invisible version of the Haggle menu to be used when EE needs to open and immediately close the Haggle Menu. This works fine, but confuses players a bit since EE's Haggle Menu conflicts with DarnUI's etc.
So if EE could just redirect the xml file that gets opened as the Haggle menu to my invisible menu instead, I would avoid having to include a standard haggle menu xml file. The question is whether this alternative file would be understood as the haggle menu and work as intended though.
If a mod uses this then does the mod require this?(like everyone who downloads has to have it)
What kyoma said. As an example, my Enhanced Economy mod has two features that requires Pluggy (read price files, write item removal log) and one feature that requires MenuQue (show Real Values - not rounded values - in Bartrer Menu when you hover over an item). But Enhanced Economy only requires those plugins if you enable those features. If you enable a feature without having the needed plugin, the feature will be disabled.
My Useful Houses mod however, requires MenuQue to work at all.