Just this week in HEL the agent (contracted agent, not SK) also ran into a roadblock trying to move my 8pm departure to the 3pm flight.

I was booked on a Plus Smart fare and when she tried the system to move me, it said it can’t find any alternative flights... of course not since for a same day departure only Plus Pro would be available.

I almost accepted not being on the 3pm flight and spend 5 hours in the miserable HEL SK lounge but the agent didn’t accept defeat and called a colleague in the back end. Together they sorted it out and 10 minutes later I boarded the 3pm flight.

kudos to the lovely lady in HEL!

so, it definitely can be done! And I never had any problems in the last two years to do so - even in cheap Plus fares.

Not sure about upgrades thought. They upgraded you because of availability on that fight. Using the upgrade to move you over to another flight might not work out.

But probably worth trying. I don’t think the gate agent will check the ticket history. Probably just look at the booking class - or actually class of service - and be done with it.