Is this possible update with use of the API a notes field, is visible at user popup
Nope, that’s not supported.
It can be useful, specially i will be able put there nicknames … from the site. Cause now few users can set up same name and email is not visible everywhere! And how to identify user then…
A patron that is subscribed to your campaign cant use two different emails to subscribe to your campaign. So you can identify the patron from there.