Package: lightdm-gtk-greeter-settings
Version: 1.2.2-2

When you use lightdm-gtk-greeter-settings to modify LightDM's greeter
and press "save", it modifies /etc/lightdm/lightdm-gtk-greeter.conf.
The problem is that (at least under Devuan Beowulf)
/etc/lightdm/lightdm-gtk-greeter.conf
is a symlink to
/etc/alternatives/lightdm-gtk-greeter.conf
which in turn is a symlink to
/etc/lightdm/lightdm-gtk-greeter.conf-devuan-cinnabar

So you end up losing the original lightdm-gtk-greeter.conf-devuan-cinnabar.