Lastly, if the above is successful, the next issue would be managing the quantities of stock available. I do not recall where in this thread or perhaps it is in a similar thread related to stocking by attributes, but there have been ways posted about how to obtain stock data for existing quantities. If that data can be obtained with the stock_id, then a similar process could be used to populate the additional stock through a SQL statement.

UPDATE `(prefix_)products_with_attributes` SET `quantity` = `quantity` + `(new quantity obtained from spreadsheet or other source)` WHERE `stock_id` = `(the stock_id value for the row in question)`;

Note: Above, the use of parantheses () is to indicate that the value is calculated/obtained from somewhere such as a spreadsheet. The parentheses are not to be included in the actual statement. Also the use of single quotes around a number is not mandatory, but seems to be recommended.

I would recommend also that if the above is successful that questions related to development of an export option of the products_with_attributes table be addressed on the easypopulate thread. A response may be to self develop which may be possible using the existing code/instruction to handle this situation, but that aspect is more about EP than it is about stock by attributes... It just happens that in this case EP became a tool to support stock by attributes.

Good luck!