function maybe_create_affiliate( $user_id, $user_tags ) {

    if ( in_array( 'Tag Name', $user_tags ) && ! affwp_is_affiliate( $user_id ) ) {

        $args = array(
            'user_id' => $user_id,
        );

        affwp_add_affiliate( $args );

    }

}

add_action( 'wpf_tags_modified', 'maybe_create_affiliate', 10, 2 );