Hi Vivek,
There is no way to rewrite the secret key. They are locked at the time of manufacturing making each zymkey unique by design.
Using true random number generator (TRNG) feature, you can create your own secret key, then lock it to the system using the zymkey lock method. The newly generated key is then used to encrypt/decrypt messages, and is protected by the unique, secret key onboard the zymbit trust module (zymkey).
Evan