Alicia here, from the Shopify Guru team!
Happy to provide some options for you! There are a couple of different ways through Shopify that you could accomplish this - through product CSV as well as through the Bulk Editor. The product CSV option will have you export all of the products that you need to add a UPC code to - this will export those products into a CSV file that can be opened with whatever program you have available to you for a spreadsheet. You can then enter the UPC for each product within the file and import that back in. The benefit of this option is that you can update this information outside of your Shopify Admin, so that if any other updates need to take place, you don't have to interupt your UPC addition. The Bulk Editor will allow you to select all of the products that you'd like to add a UPC code to, and remain within the Shopify Admin whilie you update that.
I hope this helps, Beau! Please don't hesitate to let me know if you have any further questions at all!
All the best,
Alicia D. | Shopify Guru
I hope this isn't too late but if you have a CSV file of just your SKUs (or product handles) and UPC codes you can use our Bulk Product Editor to update everything quickly.
Once you install the app you can upload the CSV file and it will look like this:
Then just click Preview, verify that everything looks good, and start the edit. It will run in the background so you can work on other things.
If you have any questions about the app we're always here to help. Thanks!