If you delete the old product codes out of StockTrim then they won’t reappear next time you re-sync with your inventory management system or re-upload your data, and only the new ones will show.
We use the product codes to match on when reloading, to determine whether an item exists to update it, or whether it’s a new one. So if you change the product code then the system will treat it as a new product.
We generally don’t recommend changing product codes, but if you need to then when you change product codes, you’ll also need to go into StockTrim and delete the old product code, then when you re-sync the new one will be loaded correctly.
Note that if you have imported your sales orders via CSV, you'll also need to reimport your sales history with the new product codes as well. You could also alternatively set the old product codes to discontinued, and then link the demand from the new product code to the old one.