Hi there, rgerger. 

While you cant exactly add notes to the AR aging report that aren't visible to your customers and that transfer over to your excel files, I do have a work around you can do that does exactly what you need. What you'll want to do is add the notes to your memo section. This won't be shown on your invoices and then when you want to transfer them over to excel all you'll need to do is add that memo column to the report.

If you have any other questions or concerns, feel free to post here anytime. Thank you and have a lovely night.