I just tested it out...
Googling around, I ended up with this little script (called edit.sh):
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#!/bin/sh
mkdir edit
mv "$1" edit
cd edit
unzip "$1"
CONTENT='\t\t<meta property="rendition:layout">pre-paginated</meta>\n\t\t<meta name="original-resolution" content="584x754"/>'
sed -i '/<\/metadata>/i\'"$CONTENT" content.opf
zip -r "$1" .
mv "$1" ..
cd ..
rm -r edit
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and surprisingly, it seem to work

! Not sure it's really solid...

Thanks a lot for showing me the way eschwartz !