I suspect that it would fix itself... eventually. You might well have to celebrate them on their messed-up dates the first time around, but next year I bet you'll find that they fall where they are supposed to.
You can also wait for the day of the holiday, and cancel after it starts. This won't remove it permanently.
You might well find, that after the holiday passes on its messed up date, it will then show up where it should. So, say Harvestfest is coming up very soon, in the first week of Fall. As soon as you get past that date, it will probably pop right back up as the 2nd Thursday of Fall-- which is where it should be. After celebrating Winterfest in Fall, it will probably pop back up as the 2nd Wednesday of Winter, and so on.