These two methods are inherited from DataBoundControl and I don't see much use for them actually. DayPilot doesn't expose the event list anywhere (it's only available internally).
In the Pro (paid) version, there is a BeforeEventRender events that does what you want - you have a chance to modify the properties of each event (including InnerHTML).
In the Lite version, you will have to make items field visible or hook PerformDataBinding() method.