Well...certain parts certainly were not written by Moses ( like those after his death), then there is writing structure and such.
Personally I believe Moses wrote the vast majority, the rest was finished by others ( perhaps Joshua) and of course then there is the editing and copying by the scribes.
I do NOT think that the original meaning was ever altered however.
I believe the above conjecture is entirely reasonable. The problem and crucial error many make is they simply assume that if God used FAILABLE men to write down His word, then much of it (as we have it today) isn't His intended thoughts, but are merely the creative musings of mortals. But God has a plan for humanity, of which His Great Commission is a key part. And yet God is using humanity and men of His choosing to bring that about, and precisely as He wants it to unfold. So often, we get hung up on the micro of how God did this or that, and yet we miss His MACRO actions - how He IS the Creator of ALL that exists and how He is using it to write and enact the pages of human history, and how He has ALWAYS had an exact draft as to precisely how He wants it all to unfold, according to His perfect plans. And yet we get all hung up on whether God could truly have parted the Red Sea, turned water into wine, or given humanity His divinely inspired Word through often-inept men, or how He can turn precisely guide history's pages by also giving such men free will. We often only see the supposed "flaws" in God's plans, and yet we can't even accurately gauge the weather for tomorrow.
Too many times we believe in the either/or thing when in reality it isn't that way.
Either we trust ALL of the bible to be perfect and without error the WAY WE WANT it to be, or none of it can be trusted.
This view is wrong IMO.
We trust the bible to be what it was intended to be and in my view it was intended to point to Christ and our salvation through Him.
Your mention of the Red sea is a good one and here is why:
Did God part the Red Sea or the REED Sea?
Did He do all those miracles in Egypt?
IMO, NOT the point ( though I believe He did) because the point was that AFTER ALL they saw and witnessed the Hebrews STILL turned their back on Moses and God the first chance they had.
Yes the elements of the story that are supernatural are very important but not just to show the power of YHWH over the gods of Egypt BUT also to show how fickle and frail humans are.
Is this not echoed when Christ was abandoned? when even after He did, the miracles and even bring back the dead, His intentions were still questioned and those that were with Him all the time, still fled and lost their faith?
So many times we get caught up in the "cool" aspects of a story that we forget the meaning behind them.
I believe that the bible. like creation, is good for its purpose but not perfect.
I mean, God created creation DIRECTLY and it was good, but not perfect, so why would we expect the bible that was NOT written DIRECTLY by God and was never meant to be perfect, to be perfect?