From time to time it may be necessary to change an active calendar. However, unlike using the Calendar Generation tool you cannot simply drag and drop things in the Active Calendar.
In order to modify the active calendar it must always be done by adding or removing future identifiers on the calendar. Past (already published) identifiers cannot be changed and there is no "update" functionality provided.
In order to update an active calendar, say to move the date a given identifier is called, you must first delete the original identifier (see Deleting an Identifier) and then add the same identifier to the desired date on the calendar (see Adding an Identifier).
When moving an identifier in such a way it is important to remember to make a note of the original publish time of the identifier to ensure when adding its replacement the same publish time is used (if desired).