Gatsby Theme Catalyst was built from the ground up with component shadowing in mind. This concept is used extensively in the themes themselves and is an encouraged development pattern when creating finished sites.
All starters use component shadowing for the branding component and this same pattern can be replicated for other custom extensions of the existing themes.
For example in
gatsby-theme-catalyst-blog there are presentation components that are specifically there to be shadowed and modified without having to rewrite the data structure or GraphQL queries. This enables you to radically change the whole visual design without having to worry about the backend data structure.
See the gatsby docs for more information about component shadowing.