you can't do that (unless you hack the sources of course). Customizable menus have been requested quite a number of times and there are even more strong arguments to not support them. Nevertheless there is a patch around (if you want / can patch yourself). No idea if that still works. Be aware that patch in this context refers to source patches, i.e. you need to compile yourself to use it.
If you only want to change the title of the entry, check the wiki for language files -- you can quite easily create a custom language file that changes the naming.