Adding a traveler to Non-refundable fare cabin

[Bob Loblob]

I know we cannot change a traveler name or room, etc after booking a non-refundable fare.
 

However, If I book a single person to a standard 2-person room under a non-refundable fare, can we add a traveler at a later date?  If so, will this incur any change fees?

 

 

 

 

[Musigurl]

I recently changed travel companions for a $50 fee.