Finalizing orders "after the fact"

I have taken over the management of a small ecommerce site that uses woocommerce. Evidently they get sales via the website and do ALL processing off line. This leaves me with about 100 orders that still show as “Awaiting Processing”.
Clearly I need to work with the office to integrate woocommerce order processing in to their workflow but I don’t simply want to change the status of the existing orders as I’m afraid an email will shoot out to the customer (some from a while ago).
What would be the best way to change these orders as completed? I’m not afraid to make changes in the database directly but would value the insights of experienced woocommerce managers on this.
Thanks
john

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