How to edit a .plist file in an iPhone Xcode application?

I am kind of a newbie to this Xcode thing. I have created a Winterboard theme that disables multitasking, but I want to add that function to an Xcode iPhone app. How might I do that?

The .plist (to be exact) is /System/Library/CoreS开发者_开发百科ervices/SpringBoard.app/N18AP.plist.

I am a bit confused.

P.S. - Don't get mad if this isn't too "well-researched." :P

Thanks for the help!

P.P.S - I am using a UISwitch.

UPDATE: How do I make a DYLIB?

You will need to run your app with root permissions.

Alternatively you can write a MobileSubstrate dylib that edits the file. Your app would need to use notifications to talk to the dylib and tell it to change the value in that file.