use strict;
use XML::TreeBuilder;

my $org = <<'XML';
<FILER url='http://somewhere'><PROJECT name='test_project'/><USER email='some@email.com'/></FILER>
XML

# parse the input string
my $root = XML::TreeBuilder->new ();

$root->parse ($org);

# Insert the element
my $ins = XML::Element->new ('LOCATION', name => '1stFloor');

$root->push_content ($ins);

# Dump the result
print $root->as_XML ();