I have to repeat what the previous node already said, DO NOT TREAT XML FILES AS TEXT. Use a library that actually understands the format.

In this case one of the options is XML::Rules in the filtering mode. You would read the CSV into a hash and then process the XML file with something like

use XML::Rules;

my $filter = XML::Rules->new(style => 'filter', rules => {
  'XREF' => sub { 
    return $references{$_[1]->{_content}} ?? "Unknown reference $_[1]-
+>{_content}";
  }
});

$filter->filterfile($source_path, $result_path);
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If you do not want to process all <XREF> tags, but only those within <LinkValue> you can change the code to something like this:

my $filter = XML::Rules->new(style => 'filter', rules => {
  'XREF' => {
     qr{/LinkValue$} => sub { 
       return $references{$_[1]->{_content}} ?? "Unknown reference $_[
+1]->{_content}";
     }
# or
#    qr{/Property/LinkValue$} => sub { 
#      return $references{$_[1]->{_content}} ?? "Unknown reference $_[
+1]->{_content}";
#    }
# for only <Property><LinkValue><XREF>
   
  }
});
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