so I read that you can customise your login screen by saving the desired login screen wallpaper as com.apple.desktop.admin.png then move it to Macintosh HD > Library > Caches I'm supposed to be able to see my new login screen wallpaper when log out to log in again, but the old wallpaper is still there, though I have already deleted it. after giving up, a few log outs later, my desired wallpaper popped up. I got happy. then the next time I switch on my macbook, it's gone. so basically, the login screen wallpaper keep changing. but I only have one com.apple.desktop.admin.png file in that /caches folder. I don't know what's the problem. please help. thanks in advance!