Partners Import to Customers and Updating Transactions

Hello,

I need to set Partners on thousands of customer records and transactions. What is the best way to do that?

I tried a CSV import and was able to get the partners on the Customer record, and I selected "Update Transactions" but the transactions were only updated with the partner name and not the contribution percentage, primary, or role. Since we don't use team selling, no one other than Full Access and Admin can edit the contribution percentage, and so they can't edit and save historical transactions (which we need to do fairly often).

We were not using more than one partner per record, so we disabled the Multi-Partner Management feature. Now I've noticed that the "Update Transactions" checkbox is no longer an option on the customer record.