The Bible does not say it will be contrary and it is not contrary. Some of it is just new and different, but that is to be expected because if it was exactly the same as the NT there would be no reason for God to send another Messenger.
It does say that He will come.... All throughout the OT, whenever the end times Messiah is mentioned, it is referring to Baha'u'llah, and in the NT Jesus said He would send the Comforter and the Spirit of Truth, to complete the work He left unfinished. Jesus was a Comforter, Baha'u'llah was another Comforter.
John 14:16-17 And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever; even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you.
John 14:26 But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.
John 15:26 But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me:
John 16:7 Nevertheless I tell you the truth; It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will send him unto you.
John 16:12-14 I have yet many things to say unto you, but ye cannot bear them now. Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come. He shall glorify me: for he shall receive of mine, and shall shew it unto you.
I do not believe that Joseph Smith was a prophet of God but rather he was a seer. I don't have an issue with Paul, unless he contradicts what Jesus said. Anyone should have an issue with that if they care about Jesus.