Following Thomas’ advice I just added this to my .bash_profile:
compresspdf() {
tmpfile=$(mktemp /tmp/compresspdf.XXXXXX)
cp -p "$1" $tmpfile
gs -sDEVICE=pdfwrite -dNOPAUSE -dQUIET -dBATCH -dPDFSETTINGS=/printer -dCompatibilityLevel=1.4 -sOutputFile="$tmpfile" "$1"
mv -f $tmpfile "$1"
}
Just invoke it with: compresspdf filename