Here is how to tweak GNOME gconf-editor parameters from the command line

Use the model (this should be all on the same line!):

gconftool-2 --direct --config-source
xml:readwrite:/etc/gconf/gconf.xml.mandatory
--type Boolean --set /apps/path/to/key True

Related posts:

1. hide user list in Ubuntu Lucid 10.04 login
2. using sysctl and sysfs to tweak /proc and /sys parameters
3. Tweaking GNOME power-saving settings
4. une-gconf-default gconf file missing error while updating
5. Reclaim vertical space in Gnome!
6. working with system logs
7. Gnome network manager automatically connects to wrong networks!