I am submitting this as an enhancement, as this functionality does not exist, to my knowledge. There have been a few requests/questions around this topic, but it appears they have all been archived, or the original need has not been captured.
We receive tickets through various channels where we need to set or update the Subject for appropriateness and data governance. When tickets are received/created - the original requester email sets the ticket subject. We need the ability to set/update the subject using Automations, Scenarios, and Canned Responses. That way, when we programmatically or manually respond to the requester, the email subject line appears per our Company Policy and branding guidelines and provide consistency for data governance purposes. Furthermore, it is inefficient for end users to update these manually.