Problem: in your JSM request event configuration you would like to take different actions depending on whether the comment is created or updated.

Solution: Make use of createdEvent comment property like shown below:

#if ($issue.addedComment.createdEvent)
   Added new comment: $issue.addedComment.renderedBody 
#else
   Modified comment: $issue.addedComment.renderedBody 
#end


The createdEvent property is only valid for JSM request events (comment added - any, public comment added, private comment added)