my $ref = $xmlParser->XMLin(<<'EOX', ForceArray => 1, KeyAttr => { node => 'id' });
<?xml version="1.0" encoding="utf-8"?>
<test>
  <node id="net_1.2.3.0">
        <desc>network</desc>
  </node>
  <node id="ip_1.2.3.4">
        <desc>ipaddr</desc>
  </node>
</test>
EOX

##</code><code>##

$VAR1 = {
          'node' => {
                    'ip_1.2.3.4' => {
                                    'desc' => [
                                              'ipaddr'
                                            ]
                                  },
                    'net_1.2.3.0' => {
                                     'desc' => [
                                               'network'
                                             ]
                                   }
                  }
        };

##</code><code>##

push(@{$ref{'node'}},{
  'id'   => 'net_1.2.3.0',
  'desc' => 'network',
});

##</code><code>##

push @{$ref{node}}, {
    'net_1.2.3.0' => {
        desc => ['network']
    } 
};

##</code><code>##

<?xml version="1.0" encoding="utf-8"?>
<test>
  <node id="net_1.2.3.0">
    <desc>network</desc>
  </node>
  <node id="ip_1.2.3.4">
    <desc>ipaddr</desc>
  </node>
</test>