
When one card or drive is full the bmOS already switches to an alternate drive.
When you have dropped frames, you can select to stop recording or let it continue to record to the same drive. It seems you would like to identify an alternate card to be used when you encounter dropped frames and don’t want to stop recording.
That could be useful when the alternate card is just as capable as the original drive.
Personally I always Stop Recording so I’m aware something has gone wrong and I need to fix it.