Transactions Mass Update

I've run into a problem that I cannot find a good solution for.

We have 300+ transactions (sales orders/invoices/fulfillments/purchase orders/etc.) that have the wrong item associated on them. The old employees used the wrong item to fulfill orders. Now, in trying to get our records to sync up, I am wanting to do a mass update in which the wrong item is swapped out for the correct item. And this needs to be followed through the entire process. We just spent ~2 months entering 500+ sales orders, fulfillments, purchase orders, and invoices that were not originally in the system. We don't want to have to do that again as the sales orders and