Wow, you totally rewrote the passage to fit a reformed theology bias. But I checked and it still says they were enlightened and tasted of the heavenly gift. They partook of the Holy Spirit. Are you proposing that the Holy Spirit would allow superficial unconverted and insincere men to partake of Him? Are you saying that enlightenment is superficial?
How can we have a conversation if we so radically change scripture to fit our narratives?
I in no way rewrote the passage. I am simply addressing one interpretation of those words, which defines their meaning by common practices in the church which they participated in and the benefits that were received from them. It goes like this:
Once Enlightened: had knowledge of God disclosed in the gospel message, (10:26; 1:9; 2 Cor 4:3-6)publically confessed in baptism (in early
Christian writings conversion and baptism were often termed "enlightenment".)
Tasted the heavenly gift: this phrase could be paired with "enlightenment" as a broad description of apparent conversion or it could refer to participation in the sacrament of the Lord's Supper.
Partakers of the Holy Spirit: they had some experience of the gifts of the Holy Spirit but it is not necessary to conclude that regeneration is intended. People who lack the true faith may in some sense experience the work of God without being saved. An example would be God answering the prayers of His people to heal that person even if they do not have saving faith.
Powers of the age to come: the signs and wonders that accompanied the apostolic age.
In that case, the falling away would be irreversible (1 John 5:16) Christian salvation is final (10:4) and this, if made obstinately and would be and impenitently. 1 John 2:19 tells us they were never a part of the Christian community in the first place. This is certainly a possibility and we actually do seen it happening in our world, though at that level it is probably rare. We also see men appointing themselves as pastors, teaching the things of the gospel, having all the appearance and words of being a Christian, whose sole purpose in becoming a pastor was to make money and gain influence and power, who have no saving faith at all, and do not even believe what they say. Jesus called them wolves in sheeps clothing.
On the other hand, there is the view that sees this warning in Hebrews as a hypothetical. If one were to do this, then this is what would happen. In which case the "enlightened" would mean conversion but in a hypothetical sense. And given that the author is writing to Jewish Christians, or Gentiles previously converted to Judaism before becoming Christians, (the recipients were obviously familiar with the Law and Prophets ) and they were very immature. Knowing and believing it the person and work of Christ, truly converted. But they were immature in training in righteousness---the pursuit of it, as being as important as all the other doctrines, as Christ is our righteousness. Righteousness is what is being restored. Given the history of the day, because of persecution from both unbelieving Jews and Gentile unbelievers they were both tempted to return to their old comfort, Judaism, or to the godless behavior and practice of pagans. They were discouraged, and this letter is a letter of instruction and encouragement to stand firm in the face of suffering.
In either case, and personally think the two views are not mutually exclusive, it is not a passage that is discussing whether or not a person has a choice to choose Christ.