DA comes with a "default" skin, and a "power_user" skin. The default skin.. is.. "default" (go figure). The "power_user" skin is included, but not applied. Can be easily applied throught Reseller Panel -> Skins page.
There are global skins (/usr/local/directadmin/data/skins/*) which all Resellers can use, else there are Reseller Skins (/home/resellername/skins/*) which only those "resellername" can use. You could always try making a symbolic link from /home/resname/skins/specialskin -> /special/skin .. then only create that link for selected Resellers. (not sure it works, but don't see why not)