Your first question can be solved by using the tocstyle-package included in the KOMAscript-bundle. Try
texdoc tocstyle
at an command prompt to see the documentation.
By redefining some internal variables, if I understand your question correctly, you will have the answer to your first question. Put this commands in your preamble:
\usepackage{tocstyle}
\renewcommand*{\addchaptertocentry}[2]{%
\addtocentrydefault{chapter}{\chapapp\nobreakspace #1}{#2}%
}
\usetocstyle{KOMAlike}
Your second question was:
However, I want to treat them as appendices to appear correctly in the page headings as "Appendix A. Electro..."
This be solved by using the class-option chapterprefix=true or appendixprefix=true, if I understand your question correctly.
A complete MWE, which (hopefully) solve all questions:
\documentclass[appendixprefix=true]{scrbook}
\usepackage{blindtext}
\usepackage{tocstyle}
\renewcommand*{\addchaptertocentry}[2]{%
\addtocentrydefault{chapter}{\chapapp\nobreakspace #1}{#2}%
}
\usetocstyle{KOMAlike}
\begin{document}
\tableofcontents
\blinddocument
\appendix
\blinddocument
\end{document}
If you are using \chapter in \fronmatter, remember to use the starred version to avoid a Chapter . with empty number in your Table of Contents. Also, if you are using the command \addchapin you document, use the starred version (\addchap*}.
For further reading, see page 80 in the English manual, and this discussion at the KOMAscript homepage.
NB! This code needs a recent version of komascript.
tocloftwith KOMA-Script classscrbook. See the warning message you'd get. – cabohah Jan 15 '24 at 09:33