As usually, TIMTOWTDI. For example, you can pre-hash the names from the CSV by the coordinates, then process the XML node by node picking the new name from the hash: 
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use Text::CSV_XS;
use XML::LibXML;

my %name;
my $csv = 'Text::CSV_XS'->new({allow_whitespace => 1,
                               auto_diag        => 1,
                               binary           => 1});
open my $in, '<:encoding(UTF-8)', 'test.csv' or die $!;
$csv->header($in);
while (my $row = $csv->getline($in)) {
    $name{$row->[0]}{$row->[1]} = $row->[2];
}

my $dom = 'XML::LibXML'->load_xml(location => 'test.osm');
for my $node ($dom->findnodes('/osm/node')) {
    my $tag = $node->findnodes('tag[@k="name"]')->[0];
    if (my $name = $name{ $node->{lat} }{ $node->{lon} }) {
        $tag->{v} = $name;
    } else {
        warn "No name found for $tag->{v}: @$node{qw{ lat lon }}\n";
    }
}
$dom->toFile('new.osm');

[download]

Or, you can load the XML into a DOM, then read the CSV line by line, searching the DOM for the corresponding node and renaming it: 

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

use feature qw{ say };

use Text::CSV_XS;
use XML::LibXML;

my $dom = 'XML::LibXML'->load_xml(location => 'test.osm');

my $csv = 'Text::CSV_XS'->new({allow_whitespace => 1,
                               auto_diag        => 1,
                               binary           => 1});
open my $in, '<:encoding(UTF-8)', 'test.csv' or die $!;
$csv->header($in);

my $xpath_template = '/osm/node[@lat="%"][@lon="%"]';
while (my $row = $csv->getline($in)) {
    my $i = 0;
    my $xpath = $xpath_template =~ s/%/$row->[$i++]/gr;
    my $node = $dom->findnodes($xpath)->[0];
    if ($node) {
        my $tag = $node->findnodes('tag[@k="name"]')->[0];
        $tag->{v} = $row->[2];
    } else {
        warn "@$row missing in XML\n";
    }
}
$dom->toFile('new.osm');

[download]

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: Update XML Values using two primary keys by choroba
in thread Update XML Values using two primary keys by pratikpooja

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