Hello and welcome back,
To overwrite the add event form, you will need to create a template overwrite as outlined in our Themer’s Guide. The template you need to overwrite (edit-event.php) is located in the-events-calendar-community-events/src/views/community.
In response to your second question: that may be a question more suited for the author of the like buttons. I’m not sure how the plugin inserts the appropriate code, but they should have insight on that.
I hope I’ve provided enough information to get you started on the template override. Let me know how it goes and thanks for choosing PRO.