I don't like your @ARGV trick. I know what it does but it unnecessarily distracts from the main topic. Also it's probably better to undef($twig) than to assign zero to it. It does the same, but I'd rather undef the variable that's supposed to contain an object than set it to a number.

And of course, it would not be me if I did not promote XML::Rules whenever there's a chance:

use strict;
use warnings;
use XML::Rules;

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

my $parser = XML::Rules->new (
  style => 'filter',
  rules => {
    _default => 'raw',
    elt => sub {
      $_[1]->{attr} = 'updated';
      return $_[0] => $_[1]
    },
  }
);

#$parser->filterfile('temp.xml', 'temp-new.xml');
open my $OUT, '>', 'temp-new.xml' or die;
$parser->filterfile('temp.xml', $OUT);
close $OUT;

open my $IN, '<', 'temp-new.xml' or die;
print "::$_" while <$IN>;
[download]

Choose whichever you like better.
The line I commented out would only work in the not yet released version.