use warnings;
use strict;
use Data::Dumper;

$Data::Dumper::Sortkeys=1;

my $data = {
          'DATE' => '2013-04-25',
          'TW' => '1',
          'REF' => '1234567',
          'ACC' => '33456790'
        };

$data->{DOC} = 'EMAIL';
print Dumper($data);

__END__

$VAR1 = {
          'ACC' => '33456790',
          'DATE' => '2013-04-25',
          'DOC' => 'EMAIL',
          'REF' => '1234567',
          'TW' => '1'
        };