Sandbox Restrictions
Tweaks that create or edit files from a sandbox application outside the app’s container is no longer allowed
Use an XPC method to communicate with SpringBoard from the sandbox application
See CPDistributedMessagingCenter for some example code.
This way you could communicate with a SpringBoard class to get it to save or create your files
You would need to add AppSupport framework in your makefile
XXX_FRAMEWORKS = AppSupport
After the v1.1 Pangu Untether update it is no longer possible to save/create/modify the preferences from Sandboxed applications in “atomically” mode.
You will get something like this: