You don’t understand, this has nothing to do with SHA256 for mining after crypto. You need to sign a transaction with a private key. Quantum crypto makes all current private keys public.

This means you need to pick some date where everyone with a private key needs to create a new key under a new system. Then before quantum crypto is available they need to make this transaction from their old wallet using an old key to a new wallet with a new secure private key. And they need to do this before quantum crypto is available.