In looking at biz-class r/t travel Europe-US-Europe it seems the rules e.g. INN7C8S4 don't mention a fixed cost for voluntary changes. Before departure the ticket will be repriced using today's prices, but it's not obvious that after first flight I can't change the return date for free. The likes of QR used to charge "only" $200 or so for that privilege, while less enlightened carriers wanted $600 or simply didn't allow changes.

I must be misunderstanding the rules.