Esqueça o compiz-config-settings-manager e chegue a um terminal pressionando Ctrl + Alt + T e digite:
gsettings list-recursively org.gnome.desktop.wm.keybindings | grep --ignore-case switch
O que lhe dará uma lista de todas as chaves de troca de unidade:
org.gnome.desktop.wm.keybindings switch-to-workspace-down ['<Control><Alt>Down']
org.gnome.desktop.wm.keybindings switch-windows ['disabled']
org.gnome.desktop.wm.keybindings switch-windows-backward ['disabled']
org.gnome.desktop.wm.keybindings switch-input-source ['<Super>space']
org.gnome.desktop.wm.keybindings switch-input-source-backward ['<Shift><Super>space']
org.gnome.desktop.wm.keybindings switch-to-workspace-1 ['<Super>Home']
org.gnome.desktop.wm.keybindings switch-to-workspace-2 ['disabled']
org.gnome.desktop.wm.keybindings switch-to-workspace-3 ['disabled']
org.gnome.desktop.wm.keybindings switch-to-workspace-4 ['disabled']
org.gnome.desktop.wm.keybindings switch-panels ['<Control><Alt>Tab']
org.gnome.desktop.wm.keybindings switch-panels-backward ['<Shift><Control><Alt>Tab']
org.gnome.desktop.wm.keybindings switch-applications-backward ['<Shift><Super>Tab', '<Shift><Alt>Tab']
org.gnome.desktop.wm.keybindings switch-to-workspace-7 ['disabled']
org.gnome.desktop.wm.keybindings switch-to-workspace-5 ['disabled']
org.gnome.desktop.wm.keybindings switch-to-workspace-8 ['disabled']
org.gnome.desktop.wm.keybindings switch-to-workspace-9 ['disabled']
org.gnome.desktop.wm.keybindings switch-to-workspace-6 ['disabled']
org.gnome.desktop.wm.keybindings switch-applications ['<Super>Tab', '<Alt>Tab']
org.gnome.desktop.wm.keybindings switch-to-workspace-10 ['disabled']
org.gnome.desktop.wm.keybindings switch-to-workspace-11 ['disabled']
org.gnome.desktop.wm.keybindings switch-to-workspace-12 ['disabled']
org.gnome.desktop.wm.keybindings switch-to-workspace-left ['<Control><Alt>Left']
org.gnome.desktop.wm.keybindings switch-to-workspace-last ['<Super>End']
org.gnome.desktop.wm.keybindings switch-group-backward ['<Shift><Super>Above_Tab', '<Shift><Alt>Above_Tab']
org.gnome.desktop.wm.keybindings switch-group ['<Super>Above_Tab', '<Alt>Above_Tab']
org.gnome.desktop.wm.keybindings switch-to-workspace-up ['<Control><Alt>Up']
org.gnome.desktop.wm.keybindings switch-to-workspace-right ['<Control><Alt>Right']
use então, por exemplo:
gsettings set org.gnome.desktop.wm.keybindings switch-to-workspace-7 '<Control><Alt>KP_Home'
para definir 7 no teclado numérico para alternar para o espaço de trabalho 7.
switch-to-workspace-right
e switch-to-workspace-left
são os que você está procurando especificamente ...