Hi Leah,
Thanks for reaching out!
Unfortunately there is not currently a way to go in through the backend and change an RSVP response. (You could make the change directly in the database, but I know this isn’t an ideal solution!) I just did some testing, and it would require a bit of a customization to prevent users from changing their response within 24 hours of an event. Sorry for the bad news there! You can set a date after which new RSVPs will be disabled, but users that have already RSVP’ed can still change their response.
However, I can definitely see how these features would be useful…would you mind posting them as feature requests over in our Feature Ideas Forum? This is what we use to gauge user interest in new features and help guide future development efforts.
If you would like to give the customization a shot, our themer’s guide is the place to start! We also have a list of recommended developers if you’d like to get help with the code. I’m sorry I don’t have a better answer for you here, but if you have any other questions, please let me know!
Thanks,
Jennifer