In main(foreground) app i can use LockScreen.SetImageFileAsync method to set the lockscreen image. I couldn't able to figure out how to set the lockscreen images regular basis (every x hours) from the code. In WP8, we can use background task to update the lockscreen.
And changing lockscreen image doesn't qualify as lockscreen apps (badge/badge+text). Is it even possible with current 8.1 lockscreen API's?