Right now you can only choose one. And in fact if you map right-click to an application launcher, you lose the ability to go back to the standard menu (through the gui) because you removed the option to open “Desktop and Wallpaper”. Mouse actions aren’t configurable through system settings, not anywhere that I could find. Once you switch to the application launcher and want to go back, you have to figure out what config files to edit.
Being able to stack both, like in XFCE, would be a big improvement (and IMO should be the default), whereby the standard menu is on top when you right-click but the application launcher is immediately below. Also, it would be nice to add other things there. E.g. when I right-click I want to see something like:
Where I can swap out which text editor, etc. XFCE, a much less polished and featureful DE, already has this but KDE doesn’t 