@chaitraA8609 I don't believe the fileName attribute of the RuntimeConfig.xml for the file publisher supports anything dynamic. That being said, you could simply update the filename attribute before you start Runtime. You could write a Powershell or other command to update that value and then launch Runtime. I would not recommend that you change it though (at least not by adding the date). By keeping the file with a constant name, it allows Runtime to keep only the maximum number of files indicated in the filesToKeep attribute. If each file were a different name, you might end up with too much disk space used in a rather short amount of time. Also, the user and date are listed right at the beginning of the file (well the date certainly is, the user is present in the path to the file, but isn't specifically added and you could potentially relocate the logs to the ProgramData folder or another path where you might not see the user).
In short, if you do customize the fileName attribute of the FilePublisher, that will be the new file name.