sdcstudio

// Add the custom column to the export columns
add_filter('woocommerce_product_export_column_names', 'add_custom_gtin_export_column');
function add_custom_gtin_export_column($columns) {
$columns['global_unique_id'] = 'GTIN/UPC/EAN/ISBN';
return $columns;
}

// Populate the custom column with data for export
add_filter('woocommerce_product_export_product_row', 'add_custom_gtin_export_row', 10, 3);
function add_custom_gtin_export_row($row, $product, $product_id) {
$gtin_value = get_post_meta($product_id, '_global_unique_id', true);
$row['global_unique_id'] = !empty($gtin_value) ? $gtin_value : '';
return $row;
}

// Add the custom column to the WooCommerce importer mapping options
add_filter('woocommerce_csv_product_import_mapping_options', 'add_custom_gtin_import_mapping_option');
function add_custom_gtin_import_mapping_option($options) {
$options['global_unique_id'] = 'GTIN/UPC/EAN/ISBN';
return $options;
}

// Map the custom column to the meta key during import
add_filter('woocommerce_csv_product_import_mapping_default_columns', 'map_custom_gtin_import_column');
function map_custom_gtin_import_column($columns) {
$columns['GTIN/UPC/EAN/ISBN'] = 'global_unique_id';
return $columns;
}

// Handle the import of the custom column
add_action('woocommerce_product_import_inserted_product_object', 'save_custom_gtin_during_import', 10, 2);
function save_custom_gtin_during_import($product, $data) {
if (!empty($data['global_unique_id'])) {
$product->update_meta_data('_global_unique_id', sanitize_text_field($data['global_unique_id']));
$product->save(); // Save changes to the product object
}
}

Thank you lane, you are my lord!