Creating a new 'bodyclass'?

Sorry if this is the wrong forum to ask this, but is it possible to create a new body class in the exhibit builder plugin? Or maybe this is the wrong question to be asking. Using Omeka 2.3, Exhibit Builder 3.0, Deco theme.

What I've done is use css to import different header images for the browse, show, and item pages based upon the bodyclass. But I have several show pages for which I'd like to use different header images to reflect that page's content. . At first I was thinking of modifying the layout files, but am having doubts about approach.

Any recommendations or suggestions would be most helpful - thanks!