Here is a checklist for people maintaining their own Ghost themes based on themes we maintain at FirePress.

When a new release is available, just override the themes but not those parts. It avoids the pain of comparing each of the files and minimizes human error.

1) Custom files

/partials/custom_footer.hbs
/partials/custom_header.hbs
/package.json

2) Custom directory

/assets/css_firepress/

3) Custom default.hbs

In default.hbs, we do reference:

{{>custom_header}}
{{>custom_footer}}
custom <footer class="site-foot">

Then, follow this checklist available on our Roadmap.