#!/usr/bin/perl -w

use strict;
use warnings;

use XML::Twig;

# keep_spaces is not completely necessary, it's just
# there to keep the initial formating of the file
my $twig= XML::Twig->new( keep_spaces => 1)
                   ->parse( \*DATA)
                  ;

my $i=0;

foreach my $httpd ( $twig->root->children( 'httpd'))
  { my $config= $httpd->text;
    # do something with $config
    $httpd->set_att( config => ++$i); 
  }

$twig->print;

__DATA__
<file>
<httpd><![CDATA[
...1st piece of httpd configuration
]]></httpd>
<not_httpd />
<httpd><![CDATA[
...2nd piece of httpd configuration
]]></httpd>
</file>