Mass Change to Billable checkbox on line items on POs, Vendor Bills, and Vendor Credits

We recently realized that for a few years, unbeknownst to anyone in the company, the Items Billable by Default setting was set to on (checked) (Setup -> Accounting -> Preferences -> Accounting Preferences -> Time & Expenses Subtab -> Expenses Group). This was never intentional, and the result is over 240,000 line items on Purchase Orders, Vendor Bills, Vendor Credits, and a couple of other transaction types where Billable = Yes, so that the Items are now listed under Invoice Billable Customers.

We attempted to fix this with a CSV update, but that failed for a number of reasons (most of the transactions were in locked periods and this apparently is a G/L change, even those in open periods where the CSV gave a "success" and not a failure error, the field was not actually changed. Worse, it caused a recalculation of taxes resulting in a large number of transactions now being off by $0.01, and some foreign currency transactions being off worse because of currency revaluations. We fixed those.