Avios has booked it all into one ticket: the upgrade has been applied to both pax on the outbound, nothing voucher-related has been applied on the return, but it's all wrapped into the one ticket.

I'm content that the voucher is used, but I'd like to:
1. Cancel the return leg and be refunded that portion of Avios and taxes, leaving the one-way upgraded outbound in place
OR
2. Amend the return to depart from a different airport (£35 per pax fee, adjusted Avios/money based on tax difference and Avios cost).

Apparently I can do neither of the above, agent says. I would have thought I could.