How to set title and main matter pages independently, with memoir

I am setting up the page layout using memoir commands:

\documentclass[12pt,a4paper]{memoir}
\usepackage{lipsum}
\usepackage[charter]{mathdesign}

\begin{document}
\setlrmarginsandblock{20mm}{10mm}{*}
\checkandfixthelayout
\fixpdflayout
\lipsum[1-10]

\end{document}


This does not work properly (influences headers only). The correct way, if I recall correctly, is to put the commands before \begin{document}:

\documentclass[12pt,a4paper]{memoir}
\usepackage{lipsum}
\usepackage[charter]{mathdesign}

\setlrmarginsandblock{20mm}{10mm}{*}
\checkandfixthelayout
\fixpdflayout
\begin{document}
\lipsum[1-10]

\end{document}


This works fine. However, if I want to have different margins on the cover and in the main text, how can I achieve it? I need to call \setlrmarginsandblock after \begin{document} and then it does not work again.

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I'd set the layout for the main document, and the either make the cover separately, og have a look at \calccentering which can be combined with adjustwidth to center the cover compared to the paper, not the margins –  daleif Oct 24 '12 at 13:35
@daleif, thanks, and if you convert your comment to an answer, I will accept it. –  texnic Oct 30 '12 at 13:32

I'd set the layout for the main document, and the either make the cover separately, og have a look at \calccentering which can be combined with adjustwidth to center the cover compared to the paper, not the margins