First can I note this previous similar question -- Marginnote with geometry package -- the answer to that mis-diagnoses the cause of the problem, but gives a correct solution for memoir users.
If I use marginnote (not in memoir this time), and change the geometry, marginals are mis-set in the changed geometry. Marginpar works fine. This looks like a bug to me. How can I get marginnote to work well with geometry.
\documentclass{article}
\usepackage{marginnote}
\usepackage{geometry}
\geometry{left=2.0cm,right=3.0cm,top=2.25cm,bottom=2.25cm,heightrounded,headheight=11pt,marginparwidth=2.0cm,marginparsep=0.2cm,a4paper}
\begin{document}
%page 1
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam
voluptua.%
\marginnote{
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
eirmod tempor invidunt ut}
%page 2 (marginpar works fine)
\newgeometry{right=5.0cm,marginparwidth=3.5cm,marginparsep=0.3cm}
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
eirmod tempor invidunt ut%
\marginnote{
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
eirmod tempor invidunt ut}
%page 3
\restoregeometry
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam
voluptua.%
\marginnote{
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
eirmod tempor invidunt ut}
\end{document}