code: func (ks *KeyStore) Export(a accounts.Account, passphrase, newPassphrase string) (keyJSON []byte, err error) {
  	_, key, err := ks.getDecryptedKey(a, passphrase)
  	if err != nil {
  		return nil, err
  	}
  	var N, P int
  	if store, ok := ks.storage.(*keyStorePassphrase); ok {
  		N, P = store.scryptN, store.scryptP
  	} else {
  		N, P = StandardScryptN, StandardScryptP
  	}
  	return EncryptKey(key, newPassphrase, N, P)
  }
docs: // Export exports as a JSON key, encrypted with newPassphrase.