Someone like Sten Sture or Karl Knutsson Bonde becomes regent and then declares himself king
Given that Sten Sture died of his wounds in one of the battles half a year before the bloodbath ... i doubt he have a go at it. And Karl Knutsson Bonde (Charles VIII) died 50 years earlier, so unless either of them is ISOTed to after the time of where the bloodbath is going to be POD'ed out, i doubt that one as well