In case your desktop (or plasma crashes), use the following commands to kill and restart plasma:
kbuildsycoca4 kquitapp plasma-desktop kstart plasma-desktop
If you ever need to manually modify the Plasma configuration files,
find them in your system under
~/.kde4/share/config/plasmarc
and
~/.kde4/share/config/plasma-appletsrc
. The first
one stores global settings like the desktop theme, while the latter
stores the settings for all the individual applets.