It would be super-helpful if I could ADD new new product category to products, rather than having to export product data and add a product category to the field and then reimport and replace - which is currently how merge import is setup - not cool when managing promo items for a large store.

For example, let's say for the month of November, I want to apply a 30% discount to 100 products that are in 15 different product categories. It would be much more helpful and efficient if I could simply import a CSV with the SKUs for all the promo products and ADD a new product category of something like "NOVPROMO". Once the promo is over, I could simply delete the product category.