Joomla：为用户激活电子邮件正文添加额外字段

I am developing a joomla site, and upon registration joomla sends an email to user with an activation link. I want to change the content of that email. I have successfully created a language override for the email, but I also added some extra fields in the email. I was wondering ow to map those fields values in the email. I have changed the user plugin file and the user model in the com_user component, but nothing works. Can anyone tell me where to change that. It would be greatly appreciated.I am developing a joomla site, and upon registr