Add Inventory to existing quantity rather than assigning a new value

It would be great if there was a way to mass update inventory using a CSV file and define a boolean flag on that sheet that would indicate that the number on the sheet is to be ADDED to the existing inventory rather than replacing the current value with a new one as it currently does.

I track all of my production numbers on a spreadsheet for each day of production, I would like to be able to upload this sheet every day to keep an up to date inventory count on the site, but I can not because there is no easy way to account for each day's sales in that new number. Instead my production manager has to go update the inventory one-by-one which can be quite a lengthy and error prone process even with the inventory editor power tool.

Also on a related note it would be wonderful if there was an inventory tracking log at the product level so I could go in and look at how many inventory items were added and at what dates, this would be a great feature to go alongside the product sales history log, and would help to track and avoid data entry problems.