Instacart does allow for some level of customization and special requests for orders. Shoppers can leave notes for their personal shopper regarding substitutions or preferences when they place their order. For example, if a customer prefers a specific brand, size, or alternative product, they can note this in the "Special Instructions" section while placing the order. It is important to communicate preferences clearly so that the shopper can fulfill these requests as best as possible. However, there are limitations depending on the store and the availability of products. If a requested item is out of stock, the shopper will try to provide the closest possible alternative or follow any specific guidelines provided. Customers are encouraged to review their orders before finalizing to ensure that all preferences and requests are accurately reflected. For the most up-to-date information on this feature, customers might consider checking the current web page.