Is it possible modify the code that creates the Calendar control?

I know how to edit the calendar style to add new elements to the control. But by the moment I only know how to add new elements or delete elements, but I would like to modify an existing element.

My idea is to add a text block to the CalendarDayButton to be able to add appointments to the day, but for that i don't know hot to add a text block to this element.

Another problem is that I don't know how to modify the code that creates the calendar, I mean, the code that set the number day in each CalendarDayButton, because I need to modify this code to be able to add appointments to the new text block.

So my question is, is it possible to add appointments modfying the standard calendar and modify the code that controls what happen with the control?

Thanks.