Going Gnome - GDM Login screen background

Script for GNOME 3.16+ with GNOME Shell themes packed inside gnome-shell-theme.gresource.
Tested on Fedora 28, Fedora 29, Fedora 30 and Fedora Silverblue. But should work on any linux distro with /usr/share/gnome-shell/gnome-shell-theme.gresource file.

For non Silverblue Fedora versions:
Install from corp:
# dnf copr enable zirix/gdm-wallpaper
# dnf install gdm-wallpaper

then:
$ sudo set-gdm-wallpaper /path/to/image.png
Reboot to see changes.

OR

Download set-gdm-wallpaper.sh file and:
$ sudo set-gdm-wallpaper.sh wallpaper-gnome.png

Requires gresource binary (glib2 or glib2-devel library):
Fedora:
# dnf install glib2-devel

Fedora Silverblue version:
Fedora Silverblue have immutable file system. GDM background can be changed only by install/reinstall rpm:
# rpm-ostree install gdm-wallpaper.silver-1-3.noarch.rpm
This will change GDM wallpaper to wallpaper-gnome.png inside .rpm file. If you want change this image, you need to Build new .rpm file. See source.

Recovering / Uninstall:
If GDM load failed, then press ALT+F6 and:
# set-gdm-wallpaper.sh --uninstall
OR
# cp /usr/share/gnome-shell/gnome-shell-theme.gresource.backup /usr/share/gnome-shell/gnome-shell-theme.gresource

OR delete RPM:
# dnf remove gdm-wallpaper
OR
# rpm-ostree uninstall gdm-wallpaper

Image: https://www.opendesktop.org/s/Gnome/p/1071929/
Source: https://github.com/DimaZirix/fedora-gdm-wallpaper