Update:
It seems when editing recurring events, 'single event' modifies nothing apart from the event view that started the editing. 'following events ' modifies the whole series, before and after.
Deleting a single event in a series seems to work, though, so it's possible to delete a single event and make a replacement.
Likewise, it may be possible to terminate a series and start another for permanent changes.
Update:
It seems when editing recurring events, 'single event' modifies nothing apart from the event view that started the editing. 'following events ' modifies the whole series, before and after.
Deleting a single event in a series seems to work, though, so it's possible to delete a single event and make a replacement.
Likewise, it may be possible to terminate a series and start another for permanent changes.