Il faut au préalable avoir installé Nemo via apt.

xdg-mime default nemo.desktop inode/directory application/x-gnome-saved-search
gsettings set org.gnome.desktop.background show-desktop-icons false
gsettings set org.nemo.desktop show-desktop-icons true

Et pour vérifier :

xdg-mime query default inode/directory

Pour revenir en arrière :

xdg-mime default nautilus*.desktop inode/directory application/x-gnome-saved-search
gsettings set org.nemo.desktop show-desktop-icons false
gsettings set org.gnome.desktop.background show-desktop-icons true