To update custom letter template, use command resource/update_email_template:
svc=resource/update_email_template¶ms={"resourceId":<uint>, "subject":<text>, "body":<text>, "flags":<uint>}
| Name | Description | 
|---|---|
| resourceId | resource ID пользователя | 
| subject | letter subject | 
| body | letter body | 
| flags | use default template: 0 - yes,1 - no | 
{"error":0} /* if success */
  |