Have you heard about new Fragments Feature under Design Studio in Marketo?

Fragments - The new feature in Marketo can be used in New Email Editor. It works like a snippet and you can create you headers and footers in fragments.

Modules and snippets have been combined and replaced with fragments, which can be used absolutely anywhere – they can be dropped onto any column of any email or template.

In New Email Editor, Fragment are like snippets, not ties to any specific template, and can be dropped to any column.

Fragments have a Draft and Published status, and by default, fragments behave like No-Draft Snippets. Any updates to them automatically flow through to all templates and Emails that use that fragment, without triggering a Draft.