How do I set a default calendar-app in Android (Jelly Bean)?
Yes!  you should be able to clear the stock app from being the default calendar app by following these steps:


Go to the phone settings
select apps
scroll to the right two screen, to the 'All' section
scroll down until you can find calendar, click on it
scroll down the page and click the 'Clear defaults' button


Next time anything wants to use the calendar, you will be able to select which program you wish to use.