It is possible to conditionally stop emails from being sent. You can read this solution to learn how to conditionally send an email from an email template based on some criteria in the user variables.
In your case, you want to check if the comment is equal to a certain value or contains a certain value, so you would probably use something like this in the subject line.
#if($requesterComments.toString().contains("No review necessary"))#stop#end New access request for ${requestedForIdentityName} ready for review