In questions such as:
%% META-INFORMATION
%% \extype{schoice}
%% \exsolution{10000}
%% \exname{Regression}
%% \exshuffle{TRUE}
which comes from
\begin{solution}
\begin {answerlist}
\item True
\item False
\item False
\item False
\item False
\end{answerlist}
\end{solution}
As the correct answer changes, I want to write ‘The correct option is ’, i.e. it can be a, b, c, d or e. How can I do this?
In the minimal situation you describe I would recommend to omit the {solution} section altogether. It provides no value-added over the exsolution in the meta-information, no matter whether it is formatted as an itemized list or phrased verbally as you suggest.
In my opinion it is only worth including a {solution} if you explain why the correct answer is the correct answer. Examples for this could be the Rlogo or swisscapital exercise templates provided in the package.
In the latter case, using the R/LaTeX format for the exercises, the question is:
\begin{question}
What is the seat of the federal authorities in Switzerland
(i.e., the de facto capital)?
\begin{answerlist}
\item Basel
\item Bern
\item Geneva
\item Lausanne
\item Zurich
\item St.~Gallen
\item Vaduz
\end{answerlist}
\end{question}
For the solution it would then suffice to explain:
\begin{solution}
There is no de jure capital but the de facto capital and
seat of the federal authorities is Bern.
\end{solution}
When exshuffle is turned on, it is still easy to add a true/false {answerlist} in the {solution} but not to include the label (a/b/c/...). The former can be shuffled along with the questions but the latter is not.
Thus, if you feel it is important to include the label as well you need to do the shuffling of the {answerlist} in both {question} and {solution} yourself in the R code. See the deriv2 for an example where this is done.