use XML::Rules;

my $parser = XML::Rules->new(
	style => "filter",
	rules => [
		_default => 'raw',
		tweak => sub {
			my ($tag, $attr, undef, undef, $parser) = @_;
			if (exists $parser->{pad}{$attr->{name}}) {
				%{$parser->{pad}{$attr->{name}}} = %$attr;
				return;
			} else {
				$parser->{pad}{$attr->{name}} = $attr;
				return [$tag => $attr];
			}
		},
		tcf => sub {delete $parser->{pad}; return $_[0] => $_[1]},
	]
);

$parser->filter(\*DATA);

__DATA__
<?xml version="1.0" ?>
<tcf>
  <tweak name = "T1">
    <description>D1</description>
  </tweak>
  <tweak name = "T2">
    <description>D2</description>
  </tweak>
  <tweak name = "T3">
    <description>D3</description>
  </tweak>
  <tweak name = "T2">
    <description>This should overwrite the old T2.</description>
  </tweak>
</tcf>