XML::Twig empty_tags => 'expand' looks like it does what you want. I shortened your XML and fixed the closing "orders tag": 
use warnings;
use strict;
use XML::Twig;

my $xml = <<XML;
<orders>
  <order>
    <alt_number>2222</alt_number>
    <state>processed</state>
    <user_id>1234</user_id>
    <dd_id>54321</dd_id>
    <placed_at/>
    <total_price>449.0</total_price>
    <total_shipping_costs>90.0</total_shipping_costs>
    <discount>0</discount>
    <dd_status_code>HD</dd_status_code>
    <dd_status_desc>ORDER IS ON HOLD UNTIL 11/01/13</dd_status_desc>
    <promo_code/>
  </order>
</orders>
XML

my $twig = XML::Twig->new(
    pretty_print    => 'indented',
    empty_tags      => 'expand',
);

$twig->parse($xml);
$twig->print;


__END__


Output:

<orders>
  <order>
    <alt_number>2222</alt_number>
    <state>processed</state>
    <user_id>1234</user_id>
    <dd_id>54321</dd_id>
    <placed_at></placed_at>
    <total_price>449.0</total_price>
    <total_shipping_costs>90.0</total_shipping_costs>
    <discount>0</discount>
    <dd_status_code>HD</dd_status_code>
    <dd_status_desc>ORDER IS ON HOLD UNTIL 11/01/13</dd_status_desc>
    <promo_code></promo_code>
  </order>
</orders>

[download]

In reply to Re: How can I add missing XML open tags by toolic
in thread How can I add missing XML open tags by TheVend

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