About using mistakes as part of a code
The short answer is that such an encoding would not help with encrypting the content.

A good, modern encryption scheme should at least be secure if the attacker can choose the plaintext, let alone know what the plaintext is. Moreover, most of them are secure if the attacker can even ask for the decryption of ciphertexts of his choice (other than the actual challenge message they're trying to decrypt).

It is worth reading up on known-plaintext-attack, chosen-plaintext-attack and chosen-ciphertext-attacks.