Following up in case anyone out there has any ideas. I think the solution is to:
Set one logo for the site itself,
Add an alternative logo under Custom CSS > Manage Custom Files
Find the url of that logo
Use CSS to tell the site to use the alternative logo for tablet widths.
I *think* it would look something like this, but my CSS is wrong. Any suggestions?
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@media screen and (max-width:1024px) and (min-width:641px) { .Header-title-logo {content:url(URL OF ALTERNATIVE LOGO); }