It can be done by saving as rule into your own ruleset and class

Yes I was going to say, nothing special with Harness rules. Those are just normal rules, so you need one in your ruleset or you can also click the Private Edit button to change it for a quick test as well. 

Please refer below link:

https://community.pega.com/sites/default/files/help_v73/procomhelpmain.htm#rule-/rule-html-/rule-html-harness/main.htm

Hope this helps you.

Have tried by customizing it

Hi,

If help is required to edit the harness rule, please refer below link :

https://community.pega.com/sites/default/files/help_v62/rule-/rule-html-/rule-html-harness/main.htm