Coming full circle on this one.. I made some minor adjustments to get everything working smoothly now:

Edited UI Macro 'reference_decoration'

Where CLASS was being defined in <span>, replaced with class="${jvar_class}

Now in Each UI Macro where I was calling reference_decoration, I simply now pass through a class field to define the ICON. This allows me to define the icon for each seperate use case of g:reference_decoration (we use it in 4 or 5 different spots).

<g:reference_decoration id="${jvar_n}" field="${ref}"

   onclick="showRelatedList('${ref}'); "

   title="${gs.getMessage('Show related incidents')}" class="btn btn-default btn-ref icon-article-document"/>

For reference, all available icons can be seen using: https://<YOURINSTANCE>.service-now.com/styles/retina_icons/retina_icons.html

Thanks!
-Dan