A completely perlish way of saying what you want:

#!/usr/bin/perl -w

@holdspace = ();
while (<>) {
    if (/'(\d)'/) {
        s/^/(+$1) /g;
        s/$/;fac=$1/g;
        unshift @holdspace, $_;
    } 
    else
    {
        if (@holdspace)
        {
            print "Newline1\n", @holdspace;
            @holdspace=();
        }
        print;
    }
    if (/Line5/) {
        print "MeanLine\n";
    }
}
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Note that this does not depend on the specific digits "1", "2", or "3" - instead, it merely depends on lines containing a digit in single quotes, and that the lines to be reversed are sequential. (And that there's at least one line after the lines with single-quoted digits, though that's an easy restriction to lift) If you'd rather have something that more closely mirrored what the sed script was, (I'm guessing here, since I haven't seen the whole sed script) you could do:

#!/usr/bin/perl -w

$holdspace = "";
while (<>) {
    if (/'1'/) {
        s/^/(+1) /g;
        s/$/;fac=1/g;
        $holdspace = $_;
        $_ = "";
    }
    elsif (/'2'/) { 
        s/^/(+2) /g;
        s/$/;fac=2/g;
        $_ .= $holdspace;
        $holdspace = $_;
        $_ = "";
    }
    elsif (/'3'/) {
        s/^/(+3) /g;
        s/$/;fac=3/g;
        $_ = "Newline1\n" . $_;
        $_ .= $holdspace;
        $holdspace = "";
    }
    if (/Line5/) {
        $_ .= "MeanLine\n";
    }
    print;
}
[download]

But I personally think that's both ugly and limited in what files it applies to.