These docs are for an old release.
Info on upgrading to v5
Event::setProp
Modifies any of the non-date-related properties of an Event Object.
event.setProp( name, value )
This will cause the event to rerender. If there are other events that share the same groupId, those events’ props will be similarly modified.
To modify any of the extendedProps, use setExtendedProp.
To modify date-related properties like start, end, and allDay, use the following methods: