If you've run the OS DST update and have appointments already scheduled in the extended DST period that were created before the OS update was run, can you just open each of those calendar items - set the correct time and save it?

Q: If you've run the OS DST update and have appointments already scheduled in the extended DST period that were created before the OS update was run, can you just open each of those calendar items - set the correct time and save it? Will that rewrite the timezone information?
A: Yes, that will work.