Hi again Santhi!
You are correct, i took a look at the files. And indeed it's there that we can control the error message. But like you said it's not recommended to change anything in there.
The error message is being populated from the com.day.cq.replication.impl.servlets.CommandServlet, with the response:
Santhi Swaroop
So the only way i can see to change the message, is changing the com.day.cq.replication.impl.servlets.CommandServlet or changing the Javascript classes for /libs/cq/gui/components/common/wcm/clientlibs/wcm/js/quickpublish.js and /libs/cq/gui/components/common/admin/managepublication/clientlibs/managepublication/js/managepublication.js