How to run a script at GDM start?

# goal: Figure out how to run a command (e.g. xrandr) as GDM starts
# Specifically, I am hitting a situation as described here: 
#  - https://asus-linux.org/faq/#why-did-nvidia-mode-give-me-black-screen-with-xorg
#   "there are many ways to do this so you will need to search for the right way for your login manager."
# The problem is that on GDM, on Fedora, this seems to not be supported.

Notes:

This bug was aggressively ignored since 2012 and then closed.
https://bugzilla.redhat.com/show_bug.cgi?id=851769

There are numerous cases found in Google of people asking how to do this. 
None since 2012 show how to make it work. All seem to give up and switch DM 
or just stop asking for help.


Attemps:

# Putting this in /etc/gdm/Init/Default resulted in no file being created
echo "PWY from gdm init" > /TEST/pwy.txt

# Used similar scripts
ls -1 /etc/gdm/Init/??
/etc/gdm/Init/:0
/etc/gdm/Init/:1

# The above was tried even with SELINUX disabled (since the bug history once identified that as a cause)

# Can call ~.profile or /etc/X11/xinit/xinitrc.d/<script>.sh
# but that might not get the timing right...