It is very easy modifying SK operated flights. It is super hard with ST awards.

Last week I booked a flight close to end of business and the agent on the phone was just “done for the day”. We chatted a bit while booking my itinerary - XXX-YYY//ZZZ-XXX as ST award - and she said “awful day…. Spend hours trying to get complicated itineraries done, people shouting at her since it didn’t work out (computer says no) and in the tooling they have for ST is just terrible, was so much better for *A”. She was so happy that my request was easy… already looked for availability, gave her all the flight numbers, could spell out names using the NATO alphabet, getting the SMS code worked out fine.

it seems the change to ST didn’t make their lives easier…