直接给编辑说 附上原因 一般是可以的

后期添加作者或者通讯作者相对麻烦，但是是可以的。需要写信说一下情况，还有作者贡献，让他们帮助处理一下。

添加作者应该问题不大，我前几天想添加个通讯，挺论坛里说危险，就没敢添。

不涉嫌学术不端，有充足的理由校稿的时候是可以增加作者的，楼主可以参考以下模板：
Dear Editor,
   Our manuscript was recently accepted to be published by the Journal of xxx. We are very glad to have a chance to publish in this Journal, and that we thank very much for your help in handling our manuscript. However, we are aware that the author list is not complete. Our colleague, xxx, has indeed contributed significantly to this manuscript by (work he done)...., which we carelessly overlooked. We would just like to know whether it is possible to amend the author list now and have him added as one of the coauthor. Please kindly consider our case and inform us how to proceed. Thank you very much.
Regards,

ps. 编辑可能需要所有作者签名确认，按照要求办即可，