Thanks for your reply. What if I used your paid addon “form builder”, then created 2 different registration forms, each could have a “visible to admin only” field called “site A” on first form and “site B” on second form. Would that work? I still didn’t buy this addon so I haven’t tested it yet.
Another idea is to modify php code in your plugin code so that once the user is registered .txt file is updated with only two values “email adress from registration” and “URL refferer site that user entered registration from variable $_SERVER[‘HTTP_REFERER’]”. Thanks!