Can I edit a submission based on email feedback from the registrants?

Due to discrepancies in timing, some of the registrants need to choose other events to sign up for. They are letting me know by email and I would like to adjust their choices on jotform. How do I edit the spreadsheet?

You could allow them to edit their submissions, here's a guide that will help you with that: https://www.jotform.com/help/325-How-to-Edit-Submissions-Made-on-Your-Forms 

If you have your form integrated with Google Spreadsheet then the record should be updated automatically when the submissions is updated too.