I was also wondering about an editor, or creating my own menus under lxde - and i did find that you can use alacarte to edit your menus. it is the default opendesktop.org menu editor and does quite well for the lxde menu.
as I'm very new to lxde and this community - I just don't allow myself to edit some article directly.
Nevertheless I have two points:
is named as a directory for *.desktop-files. So isn't this a very good place to put my own app.desktop-file inside without using root?
although it exists - why using it, if I could save my desktop-files under ~/.local/share/applications?
Probably this is all very philosophical as long as I'm the only person using my PC.
I would propose the following hint:
The two locations under "/usr" should be used for applications which should be accessible (or better "includable") by every user of a system while the path and so the desktop-files inside the user's HOME-dir is/are only accessible by the corresponding user.