ADSUBCON receive replacement equipment instead of repaired equipment

We are using the DIMP ADSUBCON process to handle refurbishment at an external supplier. The scenario that we have not found a solution for is:

1. the service orders generate a PR for refurbishment of an equipment, serial number of the equipment is transferred
2. in ADSUBCON we create a PO for the subcontracting of the refurbishment
3. stock is delivered and put into vendor consignment stock using ADSUBCON
4. while being serviced the supplier determines it can't be repaired and sends a replacement instead

the "forward exchange" scenario does not fit the bill as that seems to only work when you latest at the time of PO creation decide to do a forward exchange. But in this case the decision is made after the supplier has started his work and the material is in vendor stock. The related PO fields are "locked" once the PO has moved on (in line with the SAP documentation that states that no follow up documents should exist.

Another scenario also does not fit the bill. This is changing the material serial number when doing a goods receipt based on the PO or the related inbound delivery. It does allow for the receipt of the material/serial number but then it puts the new serial number on the equipment that generated the service order (swapping the serial nr on the equipment)

The desired scenario would be

1. create service order(s)-->PR(s) -->PO for refurbishment
2. send to supplier
3. supplier notifies customer of need for scrapping old equipment and need to create new equipment
4. new material/serial number is received and either triggers the creation of a new equipment or is "attached" to the new equipment after the GR

Any suggestions on how this is supported in the ADSUBCON process would be appreciated.