use Net::EPP::Frame;

my $frame = Net::EPP::Frame::Command::Update::Contact->new;
#...
my $xpc = XML::LibXML::XPathContext->new($frame);
$xpc->registerNs('contact', 'urn:ietf:params:xml:ns:contact-1.0');
for my $name (qw(rem add)) {
        for my $node ($xpc->findnodes("//contact:$name".'[not(*|text()|@*|processing-instruction()|comment())]', $frame->documentElement)) {
            $node = $node->parentNode->removeChild($node);
        }
}

print $frame->toString(1);