Email notifications are set at the global level, so if you were to change the subject line of the event notification for "I submit a request (confirmation)" all users and projects (request queues) would be impacted. You wouldn't be able to pick and choose, as the email would trigger for every request submitted, regardless of which queue or custom form was associated.
If the request is automatically routed to a specific user or team, that person could post a comment or update with a custom message, although that would require a new manual step - unless you have Workfront Fusion.
