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Trx does have a screen that will reverse some of those mistakes. PUR > PO Receiving Processing > Reverse PO Receipt 
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The key to this screen is the Purchase Order must not be tied to an order or a project. As long as it is an inventory purchase order individual items can be reversed as needed. This
Purchase order – The purchase order number that has item that you would like to reverse on it the vendor and PO date will automatically populate in.
Rev Waybill – A Purchase order can have many waybills if it was received a different time the first one will populate in to the screen but you can type another or press F9 to choose from a list of available waybills.
Date – This is the date that the items will be un-received, the current date will default in.
Quantity Received – This is the only part of the line item detail that you can adjust, place a negative amount for the items that you would like to un-receive. If you would like no change add a zero.
Clear – the clear icon will remove the detail from the line items and the screen.
What will happen?
If the PO is an Inventory PO (No Sales Order or Project Ties), then the process will simply reverse the GL Entries for those items, as well as, the Inventory Amounts.
This is the same for Sales Order GenPOsGen POs, just note that if you shipped on the Sales Order, you will have to handle that separately if need be. Basically, the GenPO tie to the order is ignored and treated like a Stock/Inventory PO. Any adjustments needed on the Sales Order are the responsibility of the user outside of the Reversal Feature.
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Ineligible Main PO Criteria:
Waybill has been invoiced (Not allowed. No plans to change. Link to Documented Workaround coming soon...)
Project DS PO (Includes Project Site, Staging and Consolidator. This is expected to be allowed, to some degree, in the future).
None of the individual lines items are eligible (see underlined text above).
Ineligible Detail Item Criteria:
Not enough Quantity On Hand to Reverse Stock (Non-DS Lines Only)
Line is a LOT Item
So long as at least 1 detail line can be reversed, the screen will populate the receipt and prime you for reversal. You will notice that any ineligible lines will be flagged red.
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