You can have a back up set programmed.
the skreem does more then just talk to the ecu about starting the car.

and the answer to zip quote
set of keys synced to two sets of ECU & SKREEM ...one set of which coming from a scrapped car?(the currently running ECU & SKREEM and the backup ECU & SKREEM )"

You can but the issue is, if you hit the unlock or lock on the fob or try to start it. The rolling code changes it become desync. *you have to have it reprogrammed*

your better off having skreem repaired properly or our key delete done (same as people skreem delete but the right way)