Good afternoon Patricia and welcome to the Events Calendar forum!
Thank you for your interest in our products.
We’ll be glad to answer your questions.
My question is if an user creates the event, could an administrator modify the event and add RSVP functionality to the event?
Absolutely.
By the way Event Tickets Plus will also provide the additional attendee info feature to RSVP tickets.
And, if at some point you want your users to be able to manage that themselves, you will simply need to throw Community Tickets in the mix 🙂
Let me know if that helps.
Have a great day!
Geoff B.