Create a new service on DPD Portugal for WooCommerce (specifically for Switzerland, on this example), and pre-select it on the label issuing if the destination is that country

woo_dpd_portugal_available_services.php

<?php
// Add new service to DPD Portugal for WooCommerce - Specific for Switzerland
add_filter( 'woo_dpd_portugal_available_services', 'custom_add_services_ch' );
function custom_add_services_ch( $services ) {
	$services['custom_ch'] = 'Suiça';
	return $services;
}
// Each time an order is for Switzerland, choose this service by default
add_filter( 'woo_dpd_portugal_default_shipment_service_for_order', 'custom_set_default_service_ch', 10, 2 );
function custom_set_default_service_ch( $default_service, $order ) {
	if ( $order->get_shipping_country() == 'CH' ) {
		return 'custom_ch';
	}
	return $default_service;
}