How to change the login screen wallpaper in Catalina?

Just go back in the thread and read my solution that I posted as a photo/screeenshot.

I did that and never had 1 problem ever since...

Wallpaper stays the same no matter what I do no issues with that method!

Ok so I updated to Catalina 10.5.1 today and the login wallpaper reverted to the original Catalina one.

But I simply repeated the method I'd posted before and everything is back to custom now.

I'll post it again below since at this point it's kinda way back in the thread...

This works perfectly with no issues whatsoever or at least that I'm aware of.

My test is on a MBP 15" Touch Bar 2018.

Only issue/setback I've had thus far has been, as said, updating Catalina to the latest version.

Thank you so much, this method worked for me but I had to do one final step in order for it to take. After the process you described, I had to go into System Preferences > Users & Groups and change my Admin user photo. I swapped out my login wallpaper image a few times today using your method, but each time I had to do this user photo process in order for it to take. Also, just to mention this, I used Photoshop to ensure I had the proper dimensions of the source Catalina.heic image for my new login screen wallpaper. I don't know if this is mandatory though.

If you don't want to wait for OnyX:

info

Wish I was expert enough to be able to mess with the Terminal/Recovery mode and change this bloody background.

Thank you so much for this really, I will give this thing a try and get back to you!

even in Recovery Mode, the mv command fails with a 'read-only'

English would be nice....

Go back in the thread and read my post, a solution has already been found and it's easy!

The solution has already been posted, just go back in the thread.

change your profile avatar in users & Groups (edit) , and change some of the login items to clear cache.

I can confirm what applewarm posted, it worked like a charm.

This worked for me :) Thank you

Great guidance, worked for me after running the following between steps 8 & 9:

diskutil apfs updatePreboot /

''OnyX is a multifunction utility that you can use to verify the structure of the system files, to run miscellaneous maintenance and cleaning tasks, to configure parameters in the Finder, Dock, Safari, and some of Apple's applications, to delete caches, to remove certain problematic folders and files, to rebuild various databases and indexes, and more.

Release Notes

WARNING:

There is a specific version of OnyX for each major version of the operating system.

Use the specific version, and don't try to use a non-compatible version.

OnyX 3.7.0 for macOS Catalina 10.15

Requirements: Mac Intel computer running macOS Catalina 10.15.

√ This version of OnyX will be available 10-15 days after the final version of macOS Catalina is released.''

i used OnyX to change  login screen wallpaper.