Hi Steve,
Thanks for the interest in Developers license. I am not sure what you mean by extending the meta fields of the Events Calendar. The events are setup as a custom post type and you could add your own meta fields onto them and then following our Themer’s Guide:
https://theeventscalendar.com/support/documentation/events-calendar-themers-guide/
You can display the fields as you like.
If you are looking to do something else please let me know and I can answer your questions.
Thanks