sub rewrite
{
    my ($string)       = @_;
    my ($left, $right) = split /\s+/, $string, 2;

    if (my @m = $right =~ /^\d{2}(\d{2})(.*)/)
    {
        $right = $m[0] . ($m[1] =~ /^-/ ? '' : '-') . $m[1];
        // here are the new additions
        $right =~ s/\s+//g; 
        $right =~ s/-$//;

    }
    else
    {
        $right = '-' . $right unless $right =~ /^-/;
    }

    return $left . $right;
}

Please confirm that this is what you meant.
Thanks