http://qs321.pair.com?node_id=631644
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open my $fh, '+>>', $_ or die "Open failed: $!\n";
binmode $fh;
seek $fh, (-s $_) - 0xC2, 0 or die "Can't seek: $!";
printf "Found myself at position 0x%x out of 0x%x\n", tell($fh), -s $_
+;
print $fh (pack'C[4]', @vertAlign);

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Results: 
Found myself at position 0xc01501 out of 0xc015c3
Found myself at position 0x3795 out of 0x3857

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The four values still get tacked on to the END of the file instead of overwriting in the middle...