TIL You can change the subject of an Email
DISCLAIMER: I'm not here to bash Hey. In fact I wouldn't have thought of this idea if it weren't for them so great job!
I was setting up my (Non-M1) mac mini to do some work and I needed to setup my email system (currently [MailMate]). While doing this, I didn't have the "gmail" hotkeys enabled so I was trying to figure out how to enter the search field when I hit ctrl+s and I got a very interesting window.
As mentioned earlier, this was a feature that Hey was promoting as a feature.
Upon reading the caveats, I realized what MailMate was doing. Essentially it was rewriting the mail with new headers (Which was why it was saying it would appear as a new message in other clients.)
This made me realize that if this was that big of a deal you could simply forward the message to yourself with a new subject...
Sometimes the solution isn't elegant. Still it's a solution.