How to use multiple variations of a theme without installing multisite.

Hi All,

I have a very particular issue. A client wants to add a set of service pages to their website but they would like those pages to have a different nav bar, logo, menus, and footer. They still want to share users across both and the design concept is still roughly the same.

I have seen plugins that can activate many themes across different pages and directories but we need to activate two variations of the same theme.

I though about using two child themes but not quite sure how I would make global changes to the them like navigation and footer.

I would like to avoid multisite.

Any help is greatly appreciated, thanks.