Is there any safe way or changing the standard cost on SO detail lines already invoiced?

We have a situation where several SO detail lines on an order for a particular item have the wrong standard cost allocated to them.

The order lines have already been invoiced, posted, and purged to F42199 within the past week.

Can you advise the safest way to get them corrected in time for month-end (i.e. tomorrow)?

I suspect it might mean raising a Credit Order from History for the lines in question, (which by default takes the standard cost valid at the time of the original order), then entering a new order for the lines with the correct cost applied, and processing that through.