P.S. The script also—for good measure—switches out the header logos, although I designated different logos in the mixes of Protean I created.  It also adds the important "alt" attribute with my company name to both header and footer logo and sets the height and width attribute for the footer Image, so that it is slightly larger than provided for when uploading a file in lieu of a FontAwesome icon in the system navigation > footer area.

Nevertheless, I still advocate for a built-in ability to add a logo to the footer of a "mix" within Protean. It's such a nice feature already implemented for the header. Thanks for your consideration, Team Una!