Yes. You can update values, and add new attributes for existing users. All CSV uploads require you to have a column with unique identifier (Customer ID).
A few things to note:
- You can't update the customer id by
- If you leave a field blank when updating existing columns, it will result in overwriting values to unknown.
- If you update existing customers and they match the criteria for an active automated campaign, they will immediately be sent a postcard for that campaign.