\input polyset

\catcode`~=12

%\mubyte \addtilde #2a~\endmubyte
%\mubyte \addtilde #2o~\endmubyte

\def\setmubyte #1#2{\def\runseq##1{\mubyte #1 ##1~\endmubyte}\applyset{#2}}

\def\letters{abcde}
\setmubyte {\addtilde ##2} {{\letters}}
\def\addtilde#1~{\~#1}

a~la ma kota o~la ma psa

\end