Syslog configuration

I am using the Syslog endpoint n Rancher to send logs to ELK stack. What I want to do is add fields like severity, hostname, in the syslog. I need a way to update the severity of the log to what my application logs. currently it always take the severity that is set using the form. e.g. when I set the severity to Debug all logs go as Debug. Is there a option of pass through is syslog