Eh, tried posting a screenshot but don't have enough posts here to post one.

But it is indeed very misleading if the refund / change rules don't actually change if I choose Economy Flex in the change flights screen.
It quite clearly states that refund is permitted. It shows in principle the very same Economy Light/Classic/Flex options (and their rules) as when booking a completely new ticket. Wonder if they would in such case only refund the fare difference I pay for changing the flights, should I ask for a refund.

But I'm not going to chance this, although I am curious whether this would work.