You are certainly free to create and save a “password” for a non-encrypted flash drive, just like you could create and save a “password” for a shoe 
(as an example). But what would be the function of such a password? It would be useless.
Encrypted drives (or files) have a password (or PIN, key, etc.), because the very nature of encryption requires the existence of some secret piece of information that can be used for decrypting the encrypted data. In a non-encrypted flash drive (or in a shoe, to continue the above example), there is nothing to decrypt, so any “password” that you may create would serve no purpose.
Perhaps I have misunderstood your question. 