Replace pagenumber for one page in scrbook

I have a two sided scrbook where I want to replace one single page number with a special char, while the rest of the pages should remain numbered with arabic numbers. How can I achieve this?

So far I have tried it with fancyhdr and with redefining \pagemark as you can see in the MWEs, but both did not bring the intended result.

With fancyhdr the pagenumber resp. rfoot is not put in the same place as for the normal scrbook style since I use mpinclude=true:

\documentclass[twoside,mpinclude=true]{scrbook}

\usepackage[showframe]{geometry}
\usepackage{fancyhdr}
\usepackage{lipsum}

\title{Book}

\begin{document}
\maketitle

\pagestyle{fancy}
\lfoot[{:-)}]{}
\rfoot[]{{:-)}}
\cfoot{}
\section*{Acknowledgements}
I want to thank everyone.

\clearpage
\pagestyle{plain}
\lipsum

\end{document}


When I redefined \pagemark it is in the right place but I do not know, how to reset it to the previous definition.

\documentclass[twoside,mpinclude=true]{scrbook}

\usepackage[showframe]{geometry}
\usepackage{lipsum}

\title{Book}

\begin{document}
\maketitle

\lipsum[3]

\clearpage

\renewcommand{\pagemark}{:-)}
\section*{Acknowledgements}
I want to thank everyone.

\clearpage
\pagestyle{plain}
\lipsum

\end{document}


I fond an answer to the second option by redefining pagemark in this answer: https://tex.stackexchange.com/a/439431/11820

\pagemark has to be reset to \renewcommand\pagemark{\usekomafont{pagenumber}\thepage}.

\documentclass[twoside,mpinclude=true]{scrbook}

\usepackage[showframe]{geometry}
\usepackage{lipsum}

\title{Book}

\begin{document}
\maketitle

\lipsum[3]

\clearpage

\renewcommand{\pagemark}{:-)}
\section*{Acknowledgements}
I want to thank everyone.

\clearpage
\renewcommand\pagemark{\usekomafont{pagenumber}\thepage}
\lipsum

\end{document}


Note: I would not mind also receiving an answer to correctly place the pagenumber with fancyhdr in conjunction with koma scrbook mpinclude=true.