May I add an additional email (or other information) to a contact's submission form.

I generate an email most days to different groups of clients and, because those groups change, I like to generate a new CSV spreadsheet each time to gather email addresses.  However, I have people that want to add or change their contact (email) information.  I don't readily see how to affect their forms to make those changes.  Thank you for your help.

Do you mean you want to update a submission data in your form? This is possible by using the Edit Link of the submission or you can edit the submission data in the Submission page of your form. You can check this article for more information: How to Let Users Update Their Form Submissions at a Later Date. To edit a submission in the Submission page, just select on the submission you want to edit and then click Edit.