Increase header/footer margin with scrlayer-scrpage

Question

I want to edit header/footer of my document with the scrlayer-scrpage package. Here's the MWE:

\documentclass[english,BCOR=6mm,cdgeometry=twoside,DIV=12,open=right,headsepline]{tudscrbook}
\usepackage{babel}
\usepackage{isodate}
\usepackage{blindtext}
\usepackage{scrlayer-scrpage}
\begin{document}
\mainmatter
\blinddocument
\end{document}

I want header and footer to extend slightly beyond the text width. A similar question was asked yesterday (Adjust header and footer width) but there fancyhdr package is used which is not compatible with scrbook.

Edit: Also, I want to know how to format the chapter titles to look like:

Answer 1

You can use option headwidth=\textwidth+1cm:0pt. The syntax is headwidth=<width>:<offset>:<offset>, see also the KOMA-Script. If there is only one <offset> given (like in the example), this offset is used on both even and odd pages.

To get a prefix line for the chapters add class option chapterprefixline. This works for both classes scrbook and tudscrbook.

Example with scrbook:

\documentclass[english,BCOR=6mm,DIV=12,headsepline,
  chapterprefix% <- added: prefix line for chapters
]{scrbook}

\usepackage{babel}
\usepackage{isodate}
\usepackage{blindtext}

\usepackage{scrlayer-scrpage}
\KOMAoptions{headwidth=\textwidth+1cm:0pt}

\begin{document}
\blinddocument
\end{document}

Example with class tudscrbooks (uses package geometry and loads package scrlayer-scrpage):

\documentclass[english,BCOR=6mm,cdgeometry=twoside,
  %DIV=12,% page layout is calculated by package geometry
  open=right,headsepline,
  chapterprefix% <- added: prefix line for chapters
]{tudscrbook}

\usepackage{babel}
\usepackage{isodate}
\usepackage{blindtext}

\AtBeginDocument{\KOMAoptions{headwidth=\textwidth+1cm:0pt}}

\begin{document}
\blinddocument
\end{document}