How can I create a form where people can change their submissions?

Can I create a form, such as an event registration, where attendants can register for an event and then cancel or change their choices on their own without having to completely re-register.

You can add an edit submission link in the autoresponder for your form users to update their submission.

Guide:https://www.jotform.com/help/40-How-to-Let-Users-Update-Their-Form-Submissions-at-a-Later-Date

Please give it a try and let us know if this fits your requirements.