When you have set up multiple eBay accounts you can assign different listing designs to each one.
The assignment is based on listing rules level under Design & Images tab.
If you would like to install multiple free ebay listing designs then each one will have to be customised to look unique. The 2 main components that need to be edited are the header logo and footer copyright.
Although you can assign an eBay logo under settings > logos and branding this will work across all different design templates that use the ebay logo tag. To make them unique you can upload the image through ftp or under content > asset manager.
Edit the html to reflect these changes.
<div class="company-logo"><img src="[%ASSET_URL type:'logo' thumb:'ebay' %][%END ASSET_URL%]" alt="Logo"></div>
<div class="company-logo"><img alt="Logo" src="/assets/images/yourheaderimage.jpg" /></div>
<p class="muted">© [@config:COMPANY_NAME@]</p>
<p class="muted">© yourcopyrightname</p>