but if the 2nd Hash key is not present or rejected then it should get added as new tag in XML.

You can only tell if it is not present after you have trawled through all of the XML nodes, so the logic is this:

1. Loop over each XML node, if the HoH has the key then use it and then delete it from the HoH
2. After looping over all the nodes, all the remaining HoH keys are extras to be added, so loop over those keys (sorted if you like) and add them to the XML

#!/usr/bin/env perl 
use strict;
use warnings;

my @nodes = qw/foo quux baz/;
my %HoH = (
    foo => { day => 'Mon' },
    bar => { day => 'Tue' },
    baz => { day => 'Wed' }
);

# Loop over nodes
for my $node (@nodes) {
    if (exists $HoH{$node}) {
        print "Node $node found in HoH and deleted\n";
        # Do more processing here
        delete $HoH{$node};
    } else {
        print "Node $node not found in HoH\n";
    }
}

# Loop over remaining unmatched keys
for my $key (keys %HoH) {
    print "Key $key with payload $HoH{$key}->{day} not matched, so add
+ed\n";
}
[download]

Thank you for your inputs. I am now able to add node id, lat,long values in the XML file but I cannot create a new Child tag inside the new node tag to store the tag name and value.

Below is my input XML(osm file)

<?xml version='1.0' encoding='UTF-8'?>
<osm version='0.6' upload='false' generator='JOSM'>
  <bounds minlat='53.560255' minlon='8.5117942' maxlat='53.5974042' ma
+xlon='8.6024315' origin='CGImap 0.6.1 (11651 thorn-03.openstreetmap.o
+rg)' />
  <node id='-1643794' lat='53.58464144' lon='8.560693391'>
    <tag k='name' v='ASC_A_KEI_001' />
  </node>
  </osm>
[download]

My Output XML File is

<?xml version="1.0" encoding="UTF-8"?>
<osm version="0.6" upload="false" generator="JOSM">
  <bounds minlat="53.560255" minlon="8.5117942" maxlat="53.5974042" ma
+xlon="8.6024315" origin="CGImap 0.6.1 (11651 thorn-03.openstreetmap.o
+rg)"/>
  <node id="-1643795" lat="53.58464144" lon="8.560693391">
    <tag k="name" v="ASC_A_KEI_008"/>
  </node>
<node id="-1643796" lat="60.584" lon="10.560"/><node id="-1643795" lat
+="59.584" lon="9.560"/>
</osm>
[download]

Here is my updated code

my $dom = 'XML::LibXML'->load_xml(location => 'test.osm');
for my $node ($dom->findnodes('/osm/node')) {
    my $tag = $node->findnodes('tag[@k="name"]')->[0];
    my $key = "$node->{lat}.$node->{lon}";
    if (exists $HoH{$key}){
        $tag->{v} = $HoH{$key}->{name};
        $node->{id} = $HoH{$key}->{id};
        delete $HoH{$key};
    }
}

for my $key (keys %HoH){
    for my $node ($dom->findnodes('/osm')){
        my @lat_lon_key = (split /[.]/, $key);
        my $lat_key = join('.', @lat_lon_key[0,1]);
        my $lon_key = join('.', @lat_lon_key[2,3]);
        my $elm = $dom->createElement('node');
        $elm->setAttribute('id', $HoH{$key}->{id});
        $elm->setAttribute('lat', $lat_key);
        $elm->setAttribute('lon', $lon_key);
        $node->addChild($elm);
    }
    }

$dom->toFile('new_test.osm');
[download]

I have been trying to add child tags to my new node tags but I am getting error "XML::LibXML::Node::addChild() -- nNode is not a blessed SV reference".

I have tried installing the library as well but still getting error. How can I add child tags as well as align my new tags as per input? You can see that the new tags are added side by side and there is no line break. Thank you.

I got the solution to add tags and align. Below is the updated code to add tags and align.

my $dom = 'XML::LibXML'->load_xml(location => 'test.osm');
for my $node ($dom->findnodes('/osm/node')) {
    my $tag = $node->findnodes('tag[@k="name"]')->[0];
    my $key = "$node->{lat}.$node->{lon}";
    if (exists $HoH{$key}){
        $tag->{v} = $HoH{$key}->{name};
        $node->{id} = $HoH{$key}->{id};
        delete $HoH{$key};
    }
}

for my $key (keys %HoH){
    for my $node ($dom->findnodes('/osm')){
        my @lat_lon_key = (split /[.]/, $key);
        my $lat_key = join('.', @lat_lon_key[0,1]);
        my $lon_key = join('.', @lat_lon_key[2,3]);
        my $elm = $dom->createElement('node');
        $elm->setAttribute('id', $HoH{$key}->{id});
        $elm->setAttribute('lat', $lat_key);
        $elm->setAttribute('lon', $lon_key);
        my $tag = XML::LibXML::Element->new("tag");
        $tag->setAttribute('k','name');
        $tag->setAttribute('v',$HoH{$key}->{name});
        $elm->addChild($tag);
        $node->addChild($elm);   
    }
    }
my $pp = XML::LibXML::PrettyPrint->new(indent_string => "  ");
$pp->pretty_print($dom);
$dom->toFile('new_test.osm');
[download]

Thank you very for your help and inputs.