When I recently migrated from 10.3 to 10.4, I found that I couldn't change some of the recurring events in my iCal calendars. When I tried, I saw an error dialog that said the events were created by a different organizer. That organizer was me, when I was using an old email address that's no longer in my Address Book card. This behavior is new in Tiger, and very much unwanted, since these events are not shared but for my eyes only.
I could work around the problem by putting the old address back in my card, but I don't feel like keeping around every expired email address I'm ever going to have for the rest of life. Or I could cut and paste back the events, but that destroys the recurrence property. As far as I can see, there's no way to reset the address of an organizer through the UI.
Events are stored in files at ~/Library -> Application Support -> iCal -> Sources -> *.calendar -> corestorage.ics; one file for each calendar. The organizer is identified by an email address associated with each event. So I used a text editor (BBEdit) to do a multi-file search for the old address, replacing it with the new. Note that in BBEdit you must specify a search of all files, not just text files. You could also use grep and sed to do this.
It would make more sense for an organizer to be identified by a permanent attribute, such as a GUID (globally unique identifier). Just because my address changes, that doesn't mean I'm a different person. There would then be a separate database of organizers with their email addresses and other attributes, which could be changed.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2006012408314747