Here's another option:

for(split /\n/, $old_entires) {
    my($count, $num, $new_entry) = qw(0 0);
    map{$new_entry .= $_ . ($count++ < $num-1 ? '(' . $count . ')': "\
+n")}
    grep{!/\(arch\)/ && ++$num}
    split / ?\(\d\)/;
    print $new_entry;
}
[download]

Hope this helps!