They're two different things, justified and regenerate, but yes I'm up for them.
Salvation has aspects that are present, past and future.
So you think someone signed up to the covenant is undoubtedly saved, acc. Heb 10:25-29? Was every Israelite saved? If you believe that, then I have a lot less in common with you than I thought. Abraham is "
the father of the circumcised who are not merely circumcised but who also walk in the footsteps of the faith that our father Abraham had before he was circumcised." Rom 4:11 "
For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical. But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God." Rom 2:28-29 And so those set apart by the covenant are not those saved. Sorry, the two aren't the same group of people. Yes, those signed to the covenant but without faith -- they're going to be punished severely.
1 Corinthians 9:24 ... is talking about salvation?

"
Only one receives the prize"?

Well if that's true, I'm not running! Seriously, 1 Cor 9:23-27 is not talking about salvation. But that's ... kinda obvious!
Absolutely. Hebrews 10-25-29 speaks of those who have been sanctified and bought by the blood of Christ, yet turn away and the consequences are clear. These verses have always been interpreted in that manner until come the 16th C. and they proved a problem for someone`s systematic theology. Corithians 9? You are way off base. These are other verses that has been re-invented post 16th C. Here is a piece I wrote a while back. Perhaps you can attempt a systematic rebuttal.
As to Paul, he clearly did not see himself in a OSAS position. Let us look....
I do all things for the sake of the gospel, so that I may become a fellow partaker of it.
Do you not know that those who run in a
race all run, but only one receives
the prize? Run in such a way that you may win.
Everyone who competes in the games exercises self-control in all things
They then do it to receive a perishable wreath, but we an imperishable.
Therefore I run in such a way, as not without aim; I box in such a way, as not beating the air;
but I discipline my body and make it my slave, so that, after I have preached to others, I myself will not be
disqualified. 1 Corinthians 9-23-27
There is no clearer exposition in scripture and disavowal of the popular OSAS (once regenerate always regenerate, whatever you want to call it)
Note the key words.
"race...wreath (other translations "crown")
imperishable....disqualified."
Now let`s look at parallels.
The Race
Therefore, since we have so great a cloud of witnesses surrounding us, let us also lay aside every encumbrance and the sin which so easily entangles us, and let us run with endurance
the race that is set before us, fixing our eyes on Jesus, the author and perfecter of faith, who for the joy set before Him endured the cross, despising the shame, and has sat down at the right hand of the throne of God. Hebrews 12- 1,2
Precisely what Paul is speaking of in 1 Corthinians 9, the salvation "race." In this case the author of Hebrews says to "lay aside every encumbrance and the sin which so easily intangles us." Paul in Corinthians 9 says "I discipline my body and make it my slave"...
The "wreath" or crown that is "imperishable"
Do not fear what you are about to suffer. Behold, the devil is about to cast some of you into prison, so that you will be tested, and you will have tribulation for ten days Be faithful until death, and I will give you the crown of life. Rev 2-10,11
Blessed is the man who perseveres under trial, because when he has stood the
test, he will receive
THE CROWN OF LIFE that God has promised
to those that love him. James 1-12
Notice "to those that love him." This crown is not some special reward for exceptional Christians as Dispensationalist/Antinomians would like us to believe. If you miss this crown you miss final salvation! It is for "those that love him."
Disqualified
Many set on sticking to OSAS want us to believe that Paul is talking about being "disqualified" from his preaching ministry. Yet Paul speaks of running the salvation race and is concerned about becoming undisciplined and "disqualified" for final salvation or "the prize" or "wreath" that is "imperishable." The word translated "disqualified" is the Greek "adokimos" and in every single case in the N.T. is used in the context of the hellbound.
Here are two notable examples
But that which beareth thorns and briers is
rejected, and is nigh unto cursing; whose end is to be burned. Hebrew 6-8
And in other correspondence to the Corinthians
Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be
reprobates? 2 Corinthians 13-5
The evidence couldn`t be any more clear. The Apostle Paul was not living his Christian life in the context of OSAS. He viewed himself in a race that must be finished while acknowledging the hazards of giving into the flesh along the way and the potential lose of salvation. And his statements are well consistent with the tone of the N.T. as a whole and it`s forward focus on remaining in the faith.