Make certain checkout fields to be read only and disabled for registered customers in WooCommerce

HowTo Code Snippets
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Make certain checkout fields to be read only and disabled for registered customers in WooCommerce.

Snippet Type

Execute on Child Sites

Snippet

add_filter('woocommerce_checkout_fields', 'customer_readonly_checkout_billing_fields');
function customer_readonly_checkout_billing_fields( $fields ) {
    global $current_user;

    // Billing Country (select field)
    if ( ! empty($current_user->billing_country) ) {
        $fields['billing']['billing_country']['custom_attributes'] = array( 'disabled' => 'disabled' );
    }

    // Billing City (input field)
    if ( ! empty($current_user->billing_city) ) {
        $fields['billing']['billing_city']['custom_attributes'] = array( 'readonly' => 'readonly' );
    }

    return $fields;
}