Applying changes to xorg.conf without restarting
Try this from the command line:
sudo restart lightdm
sudo service lightdm restart
I am not sure what will happen if you are already running X, but it should restart it, so better close out all windows first.
See Restart X Server Ubuntu 12.04 Without Rebooting and How to kill and to start the X server? for more information.
Always a good idea to keep a copy of any configuration file before you modify it so that you can easily restore it if something goes awry.
- Backup your original xorg.conf
- Make the changes you want in xorg.conf
- Execute the command: killall X
- Ubuntu will reload the X for you with new xorg.conf