After searching the entire internet for a solution (the ones listed here did not work for my setup), I finally came up with this one:
%setup your default geometry:
\usepackage[a4paper, left=2.3cm, right=2.3cm, bottom=2.0cm, top=3.0cm]{geometry}
%use this package to get the "on-every-page-do-this-Hook" below
\usepackage{everypage}
\begin{document}
%this line registers the reset-hook:
\AddEverypageHook{\ifnum\value{page}=2\restoregeometry\else\fi}
%and this line sets your special geometry which is cleared by the hook above on page N (with N=2 in this case)
\newgeometry{left=2.3cm, right=1.7cm, bottom=2.0cm, top=9.7cm}
EDIT:
After wrapping up my proposal to a compilable example spanning several pages with lorem-ipsum-text I found it actually not working properly!
So, instead, the afterpage-package in combination with \globaldefs=1 seems like the way to go here:
\documentclass{article}
\usepackage{lipsum}
\usepackage{afterpage}
\usepackage[bottom=5cm]{geometry}
\begin{document}
\afterpage{\globaldefs=1 \newgeometry{bottom=1cm}}
\lipsum
\lipsum
\end{document}
afterpageornewgeometryfor this. Just use\enlargethispageon the first page to change its size. – David Carlisle Sep 11 '15 at 11:17\enlargethispage{-3cm}on the first page. – David Carlisle Sep 11 '15 at 11:25