Change default logon/startup/lock screen in windows 8 pro

Question

Hi,
I want to change my default logon screen, the one that appears when I boot. I have changed the lock screen within my account, but I can't change the one (that I beleive is) for the default user. I have seen some complicated steps to copy over a file
in systemdata folder for the default user profile, but It seems really awful to do it in my notebook (which is not joined to a domain, and it is Windows 8 Pro). So, is there a simple way to do it? Why my personalized lock screen isn't shown?
Regards,
MarianoC.

Answer 1

Thanks MarianoC, you got me closer to solving my lock screen problem.  Sorry about your lock screen presets issue, glad that is not an issue for me, as I see you have given up.  I wanted to post my more detailed solution description
here, since this was one of the fist places I landed while researching this.
I fixed mine by replacing the default Lock Screen image files. 
You can find them here C:\ProgramData\Microsoft\Windows\SystemData\S-1-5-18\ReadOnly  
Caution---You have to have hidden files visible, and you also have to understand how to take ownership of folders and assign ownership and permissions (it's not that difficult, search if
you don't know how).
I had 2 folders in that location W and Z;
The W folder already had my selected Lock Screen picture. 
The W folder may have been the result of a previous tweak I tried, it had the newer photo I had selected already, if your W doesn’t have your photo and you have issues maybe replace it too.
  If you don’t have a W folder I wouldn’t sweat it for now.
I had my luck with the Z folder, it contained the default space needle picture in 2 versions; dimmed and plain (I didn't look for a visual difference). 
I replaced both of them with my chosen lock screen picture.
There are 2 ways to do this;
1st is to rename your original file (add a 1 to the name, you can go back to original easier this way). Replace it with picture of your choosing with the exact same name as original. 
You must assign full permission to the system account. 
Warning. This method seems safer but I could not figure out how to assign permission to the trusted installer account, which existed previously for this file, this could inhibit some future compatibility.
2nd way preserves system and trusted installer permissions. 
Create your lock screen pictures in a separate folder, with exactly the same names as your 2 original files. 
Copy/Paste the files into the Z folder, you will get asked to replace existing. 
If you say yes it should preserve security settings but update the photo.