There are a number of ways you can achieve this:

\documentclass{article}
\usepackage{zref,refcount,alphalph,hyperref}
\makeatletter
\zref@newprop{AlphAlphcntr}[??]{\AlphAlph{\value{section}}}
\newcommand{\mylabel}[1]{\zref@labelbyprops{#1}{AlphAlphcntr}}
\newcommand{\myref}[1]{\zref@refused{#1}\zref@extract{#1}{AlphAlphcntr}}
\makeatother
\setlength{\parindent}{0pt}% Just for this example
\begin{document}
\section{A section}\label{sec:mysection}\mylabel{sec:mysection}
Section~\ref{sec:mysection}. \par
Section~\AlphAlph{\getrefnumber{sec:mysection}}. \par
Section~\myref{sec:mysection}.
\end{document}
The first reference uses \ref
, which defaults to whatever the \the<counter>
is set to (in this case, \arabic{section}
). The second reference uses the expandable \getrefnumber
provided by refcount
. The last reference uses a custom property list (with the aid of zref
) to only store and/or retrieve the \AlphAlph
-version of the section
counter.
All of the above can be extended to use hyperref
, of course.
\documentclass{...}
and ending with\end{document}
.