. and other ham fist-ed attempts while I grasp at straws. I cannot figure out for the life me what $path I should use in the setNodeText call.

Small program to test one function, like (this should probably be 3 different programs)

#!/usr/bin/perl --

use strict;
use warnings;

use XML::XPath;

Main( @ARGV );
exit( 0 );

sub Main {
    use XML::XPath;

    my $xc = XML::XPath->new(xml  => SampleXML() );
    print "ORIGINAL XML\n";
    print $xc->findnodes_as_string('/'), "\n\n";
    
    print "//blocks MATCHES MANY NODES \n";
    $xc->setNodeText( '//blocks', ' blah blah ' );
    print $xc->findnodes_as_string('/'), "\n\n";
    
    print '//cidr-map-to[@name="AKA Edge"]/blocks MATCHES MANY NODES',
+ "\n";
    $xc->setNodeText( '//cidr-map-to[@name="AKA Edge"]/blocks', ' aha 
+42 ' );
    print $xc->findnodes_as_string('/'), "\n\n";
    
    print '//cidr-map[2]/cidr-map-to/blocks  MATCHES ONE NODE', "\n";
    $xc->setNodeText( '/Product/cidr-map[2]/cidr-map-to/blocks', ' eur
+eka ' );
    $xc->setNodeText( '//cidr-map[2]/cidr-map-to/blocks', ' eureka ' )
+;
    $xc->setNodeText( '//cidr-map[@name="Prod Internal Actual"]/cidr-m
+ap-to/blocks', ' eureka ' );
    
    print $xc->findnodes_as_string('/'), "\n\n";
}


sub SampleXML {
    return <<'__XML__';
<?xml version="1.0"?>
<Product>
  <cidr-map default-datacenter="Default Datacenter" name="Internal tes
+t">
    <cidr-map-to name="AKA Edge">
      <blocks>127.0.241.174 127.0.0.181</blocks>
    </cidr-map-to>
  </cidr-map>
  <cidr-map default-datacenter="Default Datacenter" name="Prod Interna
+l Actual">
    <cidr-map-to name="AKA Edge">
      <blocks>127.0.12.1 10.0.0.1 198.168.1.1</blocks>
    </cidr-map-to>
  </cidr-map>
</Product>
__XML__
}

__END__
ORIGINAL XML
<Product>
  <cidr-map default-datacenter="Default Datacenter" name="Internal tes
+t">
    <cidr-map-to name="AKA Edge">
      <blocks>127.0.241.174 127.0.0.181</blocks>
    </cidr-map-to>
  </cidr-map>
  <cidr-map default-datacenter="Default Datacenter" name="Prod Interna
+l Actual">
    <cidr-map-to name="AKA Edge">
      <blocks>127.0.12.1 10.0.0.1 198.168.1.1</blocks>
    </cidr-map-to>
  </cidr-map>
</Product>

//blocks MATCHES MANY NODES 
<Product>
  <cidr-map default-datacenter="Default Datacenter" name="Internal tes
+t">
    <cidr-map-to name="AKA Edge">
      <blocks> blah blah </blocks>
    </cidr-map-to>
  </cidr-map>
  <cidr-map default-datacenter="Default Datacenter" name="Prod Interna
+l Actual">
    <cidr-map-to name="AKA Edge">
      <blocks> blah blah </blocks>
    </cidr-map-to>
  </cidr-map>
</Product>

//cidr-map-to[@name="AKA Edge"]/blocks MATCHES MANY NODES
<Product>
  <cidr-map default-datacenter="Default Datacenter" name="Internal tes
+t">
    <cidr-map-to name="AKA Edge">
      <blocks> aha 42 </blocks>
    </cidr-map-to>
  </cidr-map>
  <cidr-map default-datacenter="Default Datacenter" name="Prod Interna
+l Actual">
    <cidr-map-to name="AKA Edge">
      <blocks> aha 42 </blocks>
    </cidr-map-to>
  </cidr-map>
</Product>

//cidr-map[2]/cidr-map-to/blocks  MATCHES ONE NODE
<Product>
  <cidr-map default-datacenter="Default Datacenter" name="Internal tes
+t">
    <cidr-map-to name="AKA Edge">
      <blocks> aha 42 </blocks>
    </cidr-map-to>
  </cidr-map>
  <cidr-map default-datacenter="Default Datacenter" name="Prod Interna
+l Actual">
    <cidr-map-to name="AKA Edge">
      <blocks> eureka </blocks>
    </cidr-map-to>
  </cidr-map>
</Product>
[download]

Read http://w3schools.com/xpath/default.asp for gentle introduction to xpath.