The rchange parameter specifies whether recurrences are expanded in Command: storeevents, and Command: storetodos. Normally, events and todos calendar components are not expanded, so the parameter defaults to 0, which implies the series is recreated.
However, you might not want to expand recurrences when you are modifying multiple events. For example, suppose a meeting recurs every Friday starting Jan. 1, 2002. Use the following URL to change the summary of each event after Feb. 1, 2002 to changed-event.
The following example sets the rchange parameter to 0, to make the modification without adding additional events:
http://webcalendarserver/storeevents.wcap ?id=b5q2o8ve2rk02nv9t6 &calid=jdoe &uid=abcxyz &dtstart=20020201T112233Z &rrules="byday%3Dfr%3Bfreq%3Dweekly" &summary=changed-event &rid=20020201T112233Z &mod=2 &rchange=0
Note that when you are modifying a recurrence series, do not pass in rrules unless you are trying to recreate the series with a new rule.