Thanks for your quick response!
It's more/different than just seeing the list of all the changes. Actually, we don't necessarily need to see what has changed. We want to be able to point QuickBooks to a .csv/.xlsx file, have it import the data and update any existing customers with the data from that file (without creating duplicate customers in QuickBooks) and append any new customers.
Thanks for passing this on to the product engineers! If they want to see a good implementation of this, they can look at the .CSV import block in Airtable. Airtable has two .csv import options: one that isn't very capable, and the .CSV import block which is wonderful and does exactly what we want to do in QuickBooks.