I was pretty sure that writing in the main Bundle isn\'t possible in iOS ... for example an operation like :
NSString *path = [[NSBundle mainBundle] pathFor
The example is for OS X, which isn't quite as strict with permissions as iOS.
I'd be surprised if you are able to do that for much longer (if you can at all now) in a Mac App Store application bundle, though.
It could be worth filing a bug regarding the documentation.