documentclass{scrbook} % KOMA-Script book
usepackage[T1]{fontenc}
%usepackage[style=arsclassica, parts=false]{classicthesis}

begin{document}

tableofcontents

defaaa{a}
DeclareRobustCommand*{bbb}{defaaa{b}}

chapter[a]{aaabbbaaa}

end{document}

documentclass{scrbook} % KOMA-Script book
usepackage[T1]{fontenc}
usepackage[style=arsclassica, parts=false]{classicthesis}

begin{document}

tableofcontents

defaaa{a}
DeclareRobustCommand*{bbb}{defaaa{b}}

chapter[a]{aaabbbaaa}

end{document}

part{text aclForParts{acronym_label} text}

newcommand{command}[1]{%
    GlsXtrIfUnusedOrUndefined{#1}{commandhelper{#1}}{commandprf{#1}}%
} % some complicated formatting construction to be used in text body

DeclareRobustCommand*{switchcommand}{%
    renewcommand{command}[1]{glsentrylong{##1}}%
} % switch to simple unformatted variant for part titles

newcommand{aclForParts}[1]{%
    begingroup
        switchcommand
        glslink{#1}{%
            MakeTextUppercase{%
                glsentrylong{#1}%
            }%
        }
    endgroup
}