Answered by : depressed-duck-lgm74uiin99x

rewrite <name_of_the_rule> { set("<string to include>", value(<field name>));
};

Source : https://www.syslog-ng.com/technical-documents/doc/syslog-ng-open-source-edition/3.30/administration-guide/68 | Last Update : Sat, 03 Sep 22