\documentclass{oblivoir}
\makeatletter
\def\ksnamedef#1{\@namedef{#1}}
\makeatother
\ksnamedef{contentsname}{AAA}
\begin{document}

\tableofcontents

\renewcommand\contentsname{BBB}

\tableofcontents

\section{aaa}
\section{bbb}
\section{ccc}
\end{document}