I'm not sure I quite understand your question. You can dynamically build a Python dictionary. You can also shuffle the letters around. As long as the cipher is the same on both ends you can encrypt and decrypt messages on both ends.

I added a library to the blog post which has a function called random_monoalpha_cipher() which may be used to dynamically generate a cipher.

If this cipher was shared between two agents, computers, or people, it could be used to encrypt or decrypt messages.