From what I know about Immobiliser 3, the data is held on an eeprom in the cluster (with matching data in an eeprom in the ECU). If the cluster eeprom can be read and written on the board like the ECU one can, it should be relatively straightforward to read all the data from your current cluster and write it back to a replacement, without harming the original.
I would say that's much lower risk than swapping the actual chip, since with a clone you still have the old working cluster.
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