Some airlines are willing to reverse the posting when they have made a mistake, which would open up for making a retro claim on another airline. It would be down to the service mindedness of United whether they are willing (and able) to do that for you. The flight would go back to the Star Alliance system as uncredited, and you could do a retro claim to SK.
It is not just a long shot to make it happen, it is most likely an uphill struggle of dimensions.