use strict;
use warnings;
use Data::Dumper;
use XML::Simple;
my $xml = <<XML;
  <Data>    
    <Root1>
        <TBLA>    
            <NEW1>
                <KEY>KEY6</KEY>
            </NEW1>              
            <NEW2>
                <KEY>KEY9</KEY>
                <KEY>KEY10</KEY>
            </NEW2>              
            <MODIFIED>
                <KEY name ="KEY1">
                    <COLA>
                        <oldvalue>A</oldvalue>
                        <newvalue>B</newvalue>    
                    </COLA> 
                    <COLB>    
                        <oldvalue>D</oldvalue>    
                        <newvalue>E</newvalue>     
                    </COLB>
                </KEY>
                <KEY name ="KEY3">
                    <COLX>
                        <oldvalue>M</oldvalue>
                        <newvalue>N</newvalue>    
                    </COLX> 
                </KEY>
            </MODIFIED>     
        </TBLA>
    </Root1>        
    </Data>
XML

my $ref = XMLin( $xml );
print Dumper($ref);
print XMLout( $ref, RootName=>"Data" );

##</code><code>##

<Data>
  <Root1 name="TBLA">
    <MODIFIED name="KEY">
      <KEY1 name="COLA" newvalue="B" oldvalue="A" />
      <KEY1 name="COLB" newvalue="E" oldvalue="D" />
      <KEY3 name="COLX" newvalue="N" oldvalue="M" />
    </MODIFIED>
    <NEW1 KEY="KEY6" />
    <NEW2>
      <KEY>KEY9</KEY>
      <KEY>KEY10</KEY>
    </NEW2>
  </Root1>
</Data>