Self-hosting with custom newsletter templates?

I’m starting a newsletter, and I’d like to use a custom email template I’ve designed to replace all the transactional user emails as well as the newsletter.

Currently, am self-hosting via Digital Ocean’s Ghost droplet and can modify the template files directly there, but, going forward, I’d have to manually track, update and modify these templates each time Ghost pushed a new feature set.

Wondering if anyone has advice on how to best manage this.

Thanks, Davis.