There is absolutely no idea anywhere in Greek Christianity (i.e. Orthodoxy) that a human being's substance ("essence" is the word we use) can or will ever change into something else.
Do you believe we are saved by Christ's righteousness imputed to us, or something else?
"Didn't one of the Greeks here explain that, according to them, because Job was "perfect" it was possible for all men to become "perfect?""
Actually, he's Serbian -- except in the sense that all of us Orthodox are "Greek" because we share the legacy of the Greek-speaking early church. In any event, while I didn't read every post, I think that Kosta's main point was that if you are going to go sola scriptura, then the Bible's statement that "Job was perfect" taken literally contradicts the New Testament statement that "all have sinned" taken literally.
If you are going to interpret the former to mean something other than "Job was perfect", then the least you can do is to have a little consideration when discussing what the Orthodox Church has to say regarding the long-standing tradition of the sinlessness of the Theotokos.
But this has nothing whatsoever to do with your original statement that it is a Greek belief (which I initially thought you meant only to refer to pagan Greek belief -- apparently wrongly) that we humans can change our "substance."
"Do you believe we are saved by Christ's righteousness imputed to us, or something else?"
I am happy to discuss this question as well, which will involve a definition of terms and careful exchange of meaning.
But again, I want to finish what we started, which is, again, a very different question. Surely you know that.
If you are stating that Greek Christianity (i.e. Orthodoxy) teaches that we as humans can be transformed into a different essence (our preferred word for what the Latins call "substance"), then you are absolutely wrong, and I would be interested to read any patristic quotation or quotation from an Orthodox liturgical text that says otherwise.
Salvation/theosis does not involve becoming something other than a human being, or in changing from one essence/substance to another. If it did, there would not be such a heavy emphasis on the importance of the resurrection of the body. It does not involve us changing from a human nature to some other kind of nature -- if it did, then there would have been no reason for Christ to take on human nature. If humans were going to escape human nature and become some other kind of essence, then why would Christ have kept his human body and nature (which he still has today, with which he will return in glory to earth, and which he will keep for all eternity?)
If you understand the very basic Orthodox concepts of essence, nature, hypostasis (person), and energies, then you know this, and are just poking at me. If you don't understand what we believe, then ask -- it's much more efficient that way than for you to tell me what I believe, only for me to have to correct you.