Can you have a field that is for internal use only? And if so, how do you add it?

I need to add a field that only I can see/edit on the back end and the registrant woudln't have access to the data or the field header, either upon submission, editing their response, or any other way. Is this doable? And if so, how?

Yes it is possible to achieve your requirement. Please add a short text entry field in form and hide it. When your users access the form to submit it, the hidden field will not be displayed. But when you as a form owner login to your JotForm account and edit submission, the field which are manually hidden will not be displayed to you. Please check the screenshot below:

Hope this helps.

Do get back to us if you have any questions.