Create new chapter-like section command with custom sectioning-numbering

I try to create a custom command \specialchapter that works very similar to the normal \chapter command, but uses it's own counter. And I would like for the section numbering under this ´\specialchapter to

\chapter{Normal Chapter}
\section{Section}
\subsection{Subsection}

\specialchapter{Special Chapter}
\section{Section}
\subsection{Subsection}

\chapter{Normal Chapter}
\section{Section}
\subsection{Subsection}


should result in section numbering like this:

Chapter 1: Normal Chapter
1.1 Section
1.1.1 Subsection

Special 1: Special Chapter
S1.1 Section
S1.1.1 Subsection

Chapter 2: Normal Chapter
2.1 Section
2.1.1 Subsection


The idea is to have \specialchapter on the same level as \chapter but highlight sections in those chapters with a prefix letter to make the section numbering unambiguous.

I use KOMA-Script and tried

\DeclareNewSectionCommand[%
level=0,
style=chapter,
tocstyle=chapter,
tocindent=0pt,
toclevel=0,
tocnumwidth=1.5em,
beforeskip=0pt,
]{specialchapter}
\def\thespecialchapter{S\arabic{specialchapter}}%


This creates the chapter-like command, but the sections under this command continue their numbering from the last \chapter command.

specialchapter must use the same reset list as chapter:

\makeatletter
\let\cl@specialchapter\cl@chapter% use the same reset list
\makeatother


This resets the section number, when a new specialchapter starts. But \thesection is still defined as \thechapter.\arabic{section}. This can be changed by

\newcommand*\originalthechapter{}
\let\originalthechapter\thechapter
\newcommand*\useinnumbers[2]{\gdef\thechapter{#1}}


which will work for figures, tables etc. too.

Example:

\documentclass{scrreprt}

\DeclareNewSectionCommand[%
level=\chapternumdepth,
style=chapter,
tocstyle=chapter,
tocindent=0pt,
toclevel=\chaptertocdepth,
tocnumwidth=1.5em,
beforeskip=0pt,
]{specialchapter}
\renewcommand\thespecialchapter{S\arabic{specialchapter}}%
\makeatletter
\let\cl@specialchapter\cl@chapter% use the same reset list
\makeatother

\newcommand*\originalthechapter{}
\let\originalthechapter\thechapter
\newcommand*\useinnumbers[2]{\gdef\thechapter{#1}}

\begin{document}
\tableofcontents
\listoffigures
\chapter{Normal Chapter}
\section{Section}
\subsection{Subsection}
\captionof{figure}{A figure in Normal Chapter}
\chapter{Normal Chapter}
\section{Section}
\subsection{Subsection}
\captionof{figure}{A figure in Normal Chapter}

\specialchapter{Special Chapter}
\section{Section}
\subsection{Subsection}
\captionof{figure}{A figure in Special Chapter}

\chapter{Normal Chapter}
\section{Section}
\subsection{Subsection}
\captionof{figure}{A figure in Normal Chapter}
\end{document}
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