\documentclass{article}
\usepackage{testmods}
\makeatletter
% This already works
\newcommand\keydef[2][]{\omdaddkey{#1}{#2}%
\@ifundefined{mod@id}{}{%
\expandafter\g@addto@macro\this@module{\omdaddkey{#1}{#2}}}}

% this does not yet. 
\newcommand\keysdef[2][]{\@for\@I:=#1\do{\message{doing \@I}%
\omdaddkey\@I{#2}%
\@ifundefined{mod@id}{}{%
\expandafter\g@addto@macro\csname  module@defs@\mod@id\expandafter\endcsname%
{\expandafter\omdaddkey\@I{#2}}}}}

\begin{document}

\begin{module}[id=meta]
\keydef[module]{creator}
\keysdef[module,statements]{foo}
\textbf{Definition:} The {\textbf{creator}} is the author.
\end{module}

\importmodule{meta}
\begin{module}[id=test,creator=miko]
using the creator key. 
\end{module}

\begin{module}[id=test,foo=miko]
using the foo key. 
\end{module}
\end{document}

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