The ADD command adds a name/value pair to the specified set.
SET expression1, expression2 TO set
The expressions are evaluated in the context of each product in the Working Set. The string value of expression1 is the name and the string value of expression2 is the value to add to the specified set.
Example:
WHERE ebay.active LIMIT 1
ADD 'Brand', 'Estes' TO ebay.itemspecifics
LIST
The above commands select the first product with an active listing on eBay. It then adds 'Brand' => 'Estes' to the itemspecifics for the product.