Hi all, there is a file called "applications-kmenuedit.menu" in ~/.config/menus/, which allows me to add some modifications to the application launcher. Unfortunately, it doesn't cover the full range of the application launcher, such as all of the various applications which are present after installation.

Where is that "master" menu file located?

It can likely be found at /etc/xdg/menus/ - however as it is provided by your distribution, and in a very specific format, I would recommend you copy it to ~/.config/menus/ and modify the copy instead (it will override the system wide version).

Excellent, thanks again Cooks, that's just perfect!

For anyone interested in the actual content of the menu items, for example the names of the application executables, you'll find a ".desktop" file for each menu item in some other directory. In my recent Kubuntu 14.10 install, these ".desktop" files are in /usr/share/applications/kde4, though it may be a different place on your system. I think this is the only way to find out how to launch these applications from the command line.