This should do the trick (though I don't know how efficient it is):

    open OUT, ">filename" or die "can't open file for writing: $!";

    while (<DATA>) {
        my ($one, $two) = m|##(\d{4,4})## *(\d{4,4})|;
        print OUT $_ unless $one == $two;
    }

    __DATA__
    REG-NZL-PUB.1981-263 ##1981## 19810922
[download]

You'll have to modify it to use your filehandle (instead of <DATA>) that you open to read from.