The SQL statement is just for a quick, global change of all products_model to match the products_id ...
To customize the code to do this when adding a New Product, you would need to customize the file:
/admin/includes/modules/update_products.php
NOTE: and you would need to customize any other product type with its own update module ...
and around line 86 you will see:
///////////////////////////////////////////////////////
//// INSERT PRODUCT-TYPE-SPECIFIC *INSERTS* HERE //////
change to read:
// update products_model with products_id
$sql_data_array = array( 'products_model' => (int)$products_id);
zen_db_perform(TABLE_PRODUCTS, $sql_data_array, 'update', "products_id = '" . (int)$products_id . "'");
///////////////////////////////////////////////////////
//// INSERT PRODUCT-TYPE-SPECIFIC *INSERTS* HERE //////
This will add the new products_id as the products_model when adding new products ...
NOTE: even if you enter a products_model manually when adding a Product, this will override that ...
If you needed a different products_model you should be able to still edit the Product to change this manually ...