您可以使用wpmu_validate_user_signup 筛选以删除错误，然后定义WP_IMPORTING 只是为了跳过email_exist() 登记入住wp_insert_user() 功能：

add_filter(\'wpmu_validate_user_signup\', \'skip_email_exist\');
function skip_email_exist($result){
    if(isset($result[\'errors\']->errors[\'user_email\']) && ($key = array_search(__(\'Sorry, that email address is already used!\'), $result[\'errors\']->errors[\'user_email\'])) !== false) {
        unset($result[\'errors\']->errors[\'user_email\'][$key]);
        if (empty($result[\'errors\']->errors[\'user_email\'])) unset($result[\'errors\']->errors[\'user_email\']);
    }
    define( \'WP_IMPORTING\', \'SKIP_EMAIL_EXIST\' );
    return $result;
}

add_filter(\'pre_user_email\', \'skip_email_exist\');
function skip_email_exist($user_email){
    define( \'WP_IMPORTING\', \'SKIP_EMAIL_EXIST\' );
    return $user_email;
}