Changing the Desktop Background, except:

Hey everyone. I'm using a Mac Mini to display announcements on a Television in my Highschool.

I've got a network share that has a number of 1920 X 1080 jpg images in it. Each of these images is a colourful announcement with graphics and text etc.

I've set the desktop background to change every 5 seconds.

Here's the thing. 5 seconds isn't long enough.

I'd really like to have the option to change the options in the pulldown menu from 5 seconds to 10 seconds.

The ~username/Library/Preferences/com.apple.desktop.plist file has the option listed there, but the trouble is the system preference setting updates that whole file each time the desktop background changes.

In otherwords, if I change the plist file so that it should change the image every 30 seconds, the current image on the screen will stay for 30 seconds, but as soon as the next image appears, the plist file rewrites itself and sets the time change to whatever's in the system preferences pulldown, 5 seconds in my case.

My app building skills are just good enough for me to cause problems. I can see that in the /System/Library/PreferencePanes/ there's Desktop and Screensave preference there, and I can see the package contents, but I don't know what to change in there. Nor am I 100% sure that this is where I need to be to change things.

Any help would be much appreciated.

-Graham