Yep, you can make a level 1 HC toon and die right away. Once you do, you can move it to Whitemane without any faction restriction. From then on, you’re able to create both factions.
IIRC they formally announced this given HC toons routinely are moving to non HC realms and they had to get rid of the faction restriction otherwise you’d orphan your too. I believe that was when SoM toons had a chance to transfer. But I’m too lazy to look for the official blue text about it.
It’s certainly not a complete removal of the restriction, but in the context of merging servers, there’s already precedent for it!
Update: some blue post about it, regarding SoD though, but it’s more specifically talking about how FCMs remove this restriction. Which is why it works for HC → Era, or SoM to Era since it’s technically a FCM.