Comment 2 for bug 115865

Hi,

It doesn't really modify the existing one: gdm artworks are managed using alternatives.
You can find which config you are currently using with the following command: sudo update-alternatives --display gdm-config-derivative

xubuntu theme has a higher priority to ensure that it'll be the theme displayed by default on a xubuntu install (instead of the ubuntu one).
You can choose which gdm config to use with the following command(s):
sudo update-alternatives --config gdm-config-derivative # and choose the config you want

or

sudo update-alternatives --auto gdm-config-derivative # to fall back to the automatic mode