Award booking - I know you can cancel/refund one of the pax online (or with agent) and keep rest of the pax.
But can you make a change to just one of the pax keeping them in the PNR?
ie remove a departure or return portion making it a one way trip for just one pax?
My guess is you have to cancel the whole trip for that pax and rebook as a one-way separate booking.

Can you even change a single passenger return trip to a one way without cancelling and rebooking?