Yes you can do this, but you should be careful to only update the products that you want updated. Do not leave products on your list that don't need updating as you can change the inventory values by accident.
You may also want to consider a tool like MAGMI to have an easier way of updating your products.
Finally, this extension will work on your store in real time
https://www.cobby.io/
It will allow you to update your products in a spreadsheet without having the hassle of doing uploads and downloads
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