How do other companies deal with large change orders for PO (for services) and comply with SOX?

Good timing, just finished my SOX (SUX) external audit last friday. Change order for services PO it should be pretty straight forward. Create another PO with the change amount, go through usual approval workflow in any and link it to original PO (I added custom field). Another option is to close the original PO if there are no receipts against it and create a new one. If you have advanced procurement module then you can take advantage of the Contract PO or Blanket PO.

Thanks! I will have to look into how to link POs. I do option 2 currently, but if something has been billed, I will enter that line as closed on the new PO so we cannot receive against it.