automatically change geometry with KOMA-pagestyles

Question

I'm trying to change the geometry (namely the top/head height) automatically depending on the selected pagestyle.

The goal is to have a bigger backgroundpicture in the header for every new chapter. Like for example: the eyes of the tiger in regular headers and the whole head in headers with a new chapter on the page. (For the pictures I'm using layers.)

I'm using the KOMA-package scrlayer-scrpage to add the geometry to the pagestyle-pair. I puzzled this together reading the KOMA-documentation, although I have to add I did'nt read the whole thing.

The result though is that the geometry defined last is kept globaly and the text is shifted downward (even out of the page) if a geometry with bigger top-value is called:

\documentclass[11pt,a4paper]{scrreprt}
\KOMAoptions{titlepage=false,twoside, headinclude=false}

% multiple columns with the multicols-environment
\usepackage{multicol}

% language-settings similar to babel
\usepackage{polyglossia}
\setdefaultlanguage[spelling=new]{german}

% type area and margins
\usepackage[showframe]{geometry}
\geometry{left=3cm,right=2.5cm,top=10cm,head=5cm,bottom=3.75cm}
\savegeometry{plaingeometry}
\geometry{left=3cm,right=2.5cm,top=3.5cm,bottom=3.75cm}
\savegeometry{scrheadingsgeometry} 

% KOMA pagestyles
\usepackage{scrlayer-scrpage}
% should call \loadgeometry every time scrheadings is selected
\AddToLayerPageStyleOptions{scrheadings}{onselect={\loadgeometry{scrheadingsgeometry}}}
% should call \loadgeometry every time plain.scrheadings is selected, eg. with a new chapter
\AddToLayerPageStyleOptions{plain.scrheadings}{onselect=\loadgeometry{plaingeometry}}

% set headmarks
\automark[section]{chapter}

% testing
\usepackage{lipsum}

\begin{document}
\begin{multicols}{2}

    \chapter{Chapter}
    \section{Section}
    \lipsum[1]
    \subsection{{Subsection}}
    \lipsum[2-4]

    \subsubsection{Subsubsection}
    \lipsum[5-11]

    \chapter{And back again}
    \lipsum[12-17]


\end{multicols}
\end{document}

Either if you know a way to fix this, or to change geometry synchronised with changes of pagestyle I would appreciate it.(Maybe a change every time \chapter ist called would suffice to, but seems a bit to ugly to me.)

PS: First time I switched from reading to writing in this really helpfull community. I hope my autodidactic aproach doesn't hurt to bad.

Answer 1

Like Ulrike Fischer and Schweinebacke suggested I used KOMA functionality like \RedeclareSectionCommand to achive more or less, what I wanted.

Thanks for your advice, it helped me to get the bigger picture.

Thats what I've done with the picturestuff left out.

\documentclass[11pt,a4paper]{scrreprt}
\KOMAoptions{titlepage=false,twoside, headinclude=false, twocolumn}

% language-settings similar to babel
\usepackage{polyglossia}
\setdefaultlanguage[spelling=new]{german}

% type area and margins
\usepackage[showframe]{geometry}
\geometry{left=3cm,right=2.5cm,top=3.5cm,bottom=3.75cm}

\RedeclareSectionCommand[%
    beforeskip = -2.5cm plus 2mm minus 1mm,%
    afterskip  = 2.5cm plus 1mm minus 1mm%
    ]{chapter}

% KOMA pagestyles
\usepackage{scrlayer-scrpage}

% set headmarks
\automark[section]{chapter}

% testing
\usepackage{lipsum}

\begin{document}
    \chapter{Chapter}
    \section{Section}
    \lipsum[1]
    \subsection{{Subsection}}
    \lipsum[2-4]

    \subsubsection{Subsubsection}
    \lipsum[5-11]

    \chapter{And back again}
    \lipsum[12-17]

\end{document}

What exactly each of the lengths in

\RedeclareSectionCommand[% beforeskip = -2.5cm plus 2mm minus 1mm,% afterskip = 2.5cm plus 1mm minus 1mm% ]{chapter}

does, keeps slipping my mind though.