%
\def\thetitle{}
\def\thesubtitle{}
+\def\thesubsubtitle{}
\def\thecomposer{}
\def\thearranger{}
\def\theinstrument{}
% duh. LaTeX has a \title too.
\renewcommand*{\title}[1]{\def\thetitle{#1}}
\newcommand*{\subtitle}[1]{\def\thesubtitle{#1}}
+\newcommand*{\subsubtitle}[1]{\def\thesubsubtitle{#1}}
\newcommand*{\composer}[1]{\def\thecomposer{#1}}
\newcommand*{\arranger}[1]{\def\thearranger{#1}}
\newcommand*{\instrument}[1]{\def\theinstrument{#1}}
%
\newcommand*{\lilypondtitle}[1]{\def\thetitle{#1}}
\newcommand*{\lilypondsubtitle}[1]{\def\thesubtitle{#1}}
+\newcommand*{\lilypondsubsubtitle}[1]{\def\thesubsubtitle{#1}}
\newcommand*{\lilypondfooter}[1]{\def\thefooter{#1}}
\newcommand*{\lilypondhead}[1]{\def\theheader{#1}}
\newcommand*{\lilypondcomposer}[1]{\def\thecomposer{#1}}
\bfseries
\ifx\lilypondnull\thetitle\else{\huge\thetitle}\\ \fi
\ifx\lilypondnull\thesubtitle\else{\Large\thesubtitle}\\ \fi
+ \ifx\lilypondnull\thesubsubtitle\else{\large\thesubsubtitle}\\ \fi
\end{center}
\bigskip
% urg