Hi Sean,
I’d love to help but I’m not quite understanding the question. It sounds like you’ve built a custom template and you now want to provide a method for the currently logged in user to update their RSVP status via ajax. Is that correct?
If so, I do need to highlight first of all that the amount of support we can offer for custom dev issues tends to be pretty limited. That said, we always try to point folks in the right direction when we can. In this case, what have you already coded and which elements specifically do you need help with?
(Remember too that we have a list of great devs who can assist you with advanced customization work, should this turn out to be beyond the scope of support offered here on the forums: theeventscalendar.com/knowledgebase/find-a-customizer)
Thanks!