use strict;
use warnings;
use XML::Twig;

open my $XML, '>', 'temp.xml';
print $XML <<XML;
<root>
    <elt attr="wibble" />
</root>
XML
close $XML;

my $twig = XML::Twig->new (
    twig_roots => {elt => \&FixName}, twig_print_outside_roots => 1
    );

$twig->parsefile_inplace ('temp.xml', '.bak');
$twig = 0;

@ARGV = 'temp.xml';
print "::$_" while <>;


sub FixName {
    my ($t, $elt) = @_;
    
    $elt->set_att ('attr', 'updated');
    $elt->print ();
}

##</code><code>##

::<root>
::    <elt attr="updated"/>
::</root>