Can a person who has been Born Again, believe... [X]?

Can a person who has been Born Again, as required by Jesus, believe in [post false doctrine here]?

I will give my testimony on this point. When I became a believer in Christ, I had many false beliefs, (I'm pretty sure I've still got some lurking somewhere.) For instance, I thought Jesus was the Son of God meant He was not God. I accepted that as a given, having come under the influence of some JW literature I'd gotten ahold of earlier.

One day, someone said to me, Jesus is God, the Son. I said, no, he's God's son. That believer very gently took me through John chapter 1 and I saw Jesus was God in the flesh. My heart lept for joy, because this Jesus who had now come to live in me, was so great he was actually God too!

Yes, a believer can have very serious heretical beliefs. We are not saved by correct belief, else no one would be saved.

However, the regenerate one will also be amenable to the clear teaching of scripture and whether joyfully or not, will come to accept the truth as it is.