Okay, this is proving more difficult than I expected.
Commenting out that line, as Neal so helpfully suggested, only disables pcmanfm's management of the wallpaper. It still manages the desktop icons, therefore it still runs at startup.
What I wanted to do is disable pcmanfm from running at all, and to have the computer start xfdesktop in its place, using THAT to manage both the wallpaper AND the icons.
My original intent was to get this set up the way I wanted and then to UNINSTALL pcmanfm, but I didn't realize until recently that lxde-common and lxsession-lite would get uninstalled as well. one of those two contains the logout program/function, so uninstalling pcmanfm would hurt more than help (as I don't know how to build/compile my own).
Also, I've found through experimenting on my own just today that it's very easy to start with openbox and use an autostart script to start xfdesktop and my beloved lxpanel.
Because of this, I think my dilemma is mostly solved, but the logout program won't work unless pcmanfm is running, so would someone be able to point me in the right direction for building my own graphical logout program, or would anyone know of one already made that doesn't require me to install many extras? It’s got to include at least these three buttons: Shutdown, Reboot, and Logout.
Thanks for your time so far, folks. And sorry for such a long post this time!