In my opinion a good illustration would go something like this:
"Linda was with John Smith and Linda was a Smith"
As can be seen, the final clause, while identifying "Linda" as someone who shares a commonality with "John Smith" ie the concept of being "Smith", nevertheless, she is also clearly not being identified as the same PERSON as ''John Smith"
Whatever the meaning of the word "Smith" [and it clearly means a surname] in that sentence, the imposition of an indefinite article does not create a shift in MEANING regarding the word Smith,[Linda is a Smith in the same meaning as John Smith] the shift is in a nuance of expression.
I believe John, at Jo 1:1 is agruing against such teachings as Sabellianism, or Modalism, which saw the Word and the Father as the one and the same Person, he is not arguing against any concept that would be construed as bestowing Deity on the Word
Cheers