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');
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Thank you very for your help and inputs.