Premise now has a guide for creating and sharing custom variants, you can check it out on Itch at Premise: Template Creation Guide. The guide includes advice for making your variants as well as blank templates in a few different formats. There’s also a Google Slides version of the blank template, friendly for online play.
As part of creating the guide, I also created a new version, Premise: Artifact. In it, players will simultaneously create magical artifacts with powers, drawbacks, and backstories. Check it out!
If you end up creating new games, with these templates, I’d love to hear about it! Reach out and I’ll add it to the online collection of Premise games.