\IfFileExists{.lxformat_print}
{
\input{configprint}
}{
\input{configbeamer}
}

% Alternate Implementation
%
%\newif\ifformatbeamer
%
%\IfFileExists{lxformat.tex}{
%\input{lxformat.tex}
%}{
%\formatbeamertrue
%}
%
%\ifformatbeamer
%\input{configbeamer}
%\else
%\input{configprint}
%\fi