While I don't think this is what this passage is speaking of, just the same, who is it that is born again, born from God, filled with the Spirit of Christ, who then chooses to stop believing in Christ? Isn't this hypothetical? "Imagine if there were someone who was united in the Spirit with God, who then rejects God." I don't see that taught in the Bible. What I do see is just the opposite.
Are you remembering that Judas was sent out performing miracles, healings, preaching the Gospel? This did not assure his salvation.
As a Jew living under the Law, once you learned about Jesus, you couldn't just go back and sacrifice an animal as if Jesus' blood were no better than that.
As gentiles, and now, post-temple and post Levitical priesthood, there are no sacrifices period.
Much love!