my $twig = XML::Twig->new(
twig_handlers => { subfield => \&editSubfield, },
pretty_print => 'indented',
);

$twig->parse($xml);

sub editSubfield {
my ( $twig, $href) = @_;
my $text = $href->text();
$href->set_text($rcnnew) if $text eq $rcnorig;
}