Only Nagra emulator i've seen for silvercards was a very old non AU one named from Startrek (Piccard or Borg or something like that). These used a Microchip (16F876 processor) which weren't really up to Nagra AU processing and haven't been in use for that purpose for years !
The cards, once locked are locked to stay. You can erase them but then you loose all the info. You could read the info in the external EEprom but, afaik, the external EEprom wasn't actually used for anything in this application !