Attaching UPC's in bulk

[Swift2]

I reached a brick wall with Shopify customer agents on this, and was wondering if any one here can help. We have a lot of items in our store (15K+) and we're trying to attach in bulk, batches of UPC's to our items. We can't be wasting a lot time doing it one by one. The problems we face 

1. The "bulk edit" feature does not allow pasting a column of UPC's in the barcode box. 

2. Exporting gives us a messy file where 1 item is taking many rows, where only the 1st is appropriate for a UPC. Scrambling the file to get all the right rows on top (by assorting it through TRUE values) makes it un-importable. Been going back and forth over it with several reps, and they tell me it's not doable. It also failed to import after my adjustments.

Do you guys know of a way? Any app for that particular edit? I'm waiting on Matrixify to confirm but their app doesn't seem to do the job. Thank you.