I was wondering if you experts might have an idea on the best way to change the final destination or, essentially, add an extra segment on a Biz (I) class ticket.

My current itinerary is as follows:

ARN-LHR
LHR-HKG

but my desired itinerary is as follows:

ARN-LHR
LHR-HKG
(Stopover)
HKG-ICN

(If I were to ticket anew, this second itinerary is only marginally more expensive than the first itinerary)

The rebooking fee is 1500 SEK (~170USD). The cancellation fee is 3000 SEK (~340USD).

A new one way BIZ ticket from HKG TO ICN is >500 USD.

But as I understand it, re-booking allows for only date/time changes. Thus, it seems that I have only two options:

(i) Cancel by paying ~340 USD. And re-ticket the second itinerary.

(ii) Buy an independent ticket for >500 USD.

Am I missing a third option?