Best way to change a rep on a closed Invoice

I’ve just built some BAQs and reports to handle commissions to replace our old Access queries and reports. I’m trying to find a way, however, to change a rep on a closed invoice so that we can correct mistakes made in the past year or so with regards to incorrect reps. I know that I cannot use an updatable BAQ for this, but I was hoping someone has or knows of a work-around I could use. I read that someone used the Sales Order as a work around, however not all of our A/R invoices have SO numbers associated with them. I was hoping I could find a way to change the Invoice Head information if possible. Any advice is appreciated.