Answer
No — there's no way to build conditional logic (like an if/else based on database SID) directly into an email subject or body within IFS, since the email content is just plain text or HTML with no scripting/conditional capability. A practical workaround is to set the Mail Sender's content type to text/html (or create a separate HTML-capable Mail Sender specifically for the non-production environment) and have the relevant Event Actions include a distinct warning banner in the email body (for example, bold red text identifying it as a non-production message) — this has to be added to each event action's own email body individually, since it can't be driven by a single conditional rule.