X keyboards are configured in /usr/share/X11/xkb/, in the rules and symbols directories.
/usr/share/X11/xkb/symbols/gb can be linked to ~/config/gb. Likewise in symbols, base.xml and evdev.xml.
This has to be swapped on a per-desktop environment basis. KDE has various native options, Gnome requires a download of gnome-tweak-tool via apt-get.