Hi,

In Odoo, the expense account for stockable products is determined by the product category or overridden at the product level. For products tracked by lot, the default behavior posts costs to COGS when sold. You cannot dynamically change the expense account per sales order line for the same product.

For marketing giveaways or promotional freebies, the recommended approach is to create a separate product with the same category but assign its expense account to a Marketing Expense account. This product will have its own inventory and lots, allowing costs to post to the marketing expense instead of COGS.

Alternative methods include scrapping the product with costs assigned to Marketing Expense or making manual journal entries to reclassify the costs, but these are less automated. Using a separate product is the cleanest solution, keeping cost accounting correct and separate from normal COGS.

Hope it helps