I finally managed to import users (testing) into the "xf_user" table via PHPMyAdmin import. I copied the entries from another user and adjusted them (new eMail, new user_id etc). It worked. So far, so good. But: When in the frontend, the user is only displayed as "guest" instead of having the user group ids reflected as setup in the database. In the backend, I can not edit the user because if I click on the user from the user list, it jumps to the "create user" page and if I want to save changes, it follows an "user already exists" error... obviously. What am I missing? Are there other tables in the database that have influence on the board recognizing a new user? Or is there a cron job that needs to be done first? Please advise.