$comment = '-' . implode("\n-", $messages);

根据楼主的提示，成功的实现了自定义返回结果

{
  "message": "success",
  "status_code": 200,
  "data": [
    {
      "no": "88888888",
      "mobile": "13923458160",
      "id_no": "99999999",
      "name": "ColderWinter",
      "nick": "Wohoho",
      "sex": "男",
      "signature": "This is ColderWinter"
    }
  ]
}

return $this->collection($users, new UserTransformer, [], function ($resource, $fractal) {

    $fractal->setSerializer(new CustomSerializer);

});

==好