Managing the Sonoma screensaver plist
If you want to dig into the technical details, please read on…
Location: The new plist is located at
~/Library/Application Support/com.apple.wallpaper/Store/Index.plist
Making Changes: if you change the plist, nothing will happen. This is because the data that generates the plist is actually held in-memory. Through some experimentation, it has been determined that the WallpaperAgent process is managing the data. Fortunately, you can edit the plist, as long as you restart the process immediately afterwards:
killall WallpaperAgent
Note: this will cause the wallpaper (desktop background) image to briefly flash to black.