Classicthesis + Arsclassica ereditano da scrbook. Se non l’hanno disabilitato esiste allora il comando \setbibpreamble{preamble }.
Ti riporto uno stralcio della guida di koma-script (pagina 123):
http://texcatalogue.sarovar.org/entries/koma-script.html
\setbibpreamble{preamble }
The command \setbibpreamble can be used to set a preamble for the
bibliography. This can be achieved by placing the preamble before the
command for issuing the bibliography. However, it does not have to be
directly in front of it. For example, it could be placed at the begin-
ning of the document. Similar to the class options bibliography=totoc
and bibliography=totocnumbered, this command can only be success-
ful if you have not loaded a package which prevents this by redefin-
ing the thebibliography environment. Even though the natbib package
makes unauthorized use of internal macros of KOMA – Script it could be
achieved that \setbibpreamble works with the current version of natbib
(see [Dal99]).