How to Change CP Flights When Cancelled by Weather
 

So, booked a quick trip for 2 (Primary + Companion) to RDU returning Saturday, when Hurricane Matthew is expected to potentially hit NC. If return flights get cancelled, do I need to call to re-book even if booked on the Southwest.com? If I can re-book online, I'm assuming I can change mine first. The question is, can I also change my companion online going directly to that PNR?

As someone who grew up in NC, I'd keep a close eye out and potentially cancel your trip as you can do so at the last minute. The eastern half of the state is already soaked from recent rains, and rivers/creeks are high. If the storm makes landfall in wilmington as it looks today, Raleigh, etc will be in the outer bands of the storm as well. The good thing is the storm is moving slow at the moment, just seems like something you don't want to get stuck in.

On the original question: to make the change online, do you need to cancel the companion booking, then change your own, and add the companion back? I'm ready to do this because of a reduced fare.

Yes you do, exactly as you outlined.