I used the filters you suggested and I could make my adjustments just fine.
But the problem persists the moment I try to add the billing_country field. If I add the billing_country to the ‘fields’ array using this snippet:
$order['billing_country'] = array(
'type' => 'country',
'label' => __('Country', 'woocommerce'),
'placeholder' => __('Country', 'woocommerce'),
'required' => true,
'class' => array('form-row', 'form-row-wide', 'address-field', 'update_totals_on_change', 'validate-required', 'woocommerce-validated')
);
the fields are once again loaded correctly and then updated via ajax undoing all my modifications.
If I do not add the following field the checkout form is loaded as I would like it to be.