What did Christ mean when He said "It is finished?" That His mission of providing the means of salvation for all Humanity was finished. You bet!
Every saved individual once had not received mercy, therefore they were not chosen before their creation, because then they would have always received mercy from conception.
When God chooses an individual to be "His people" they become part of His people, and therefore to be "not a people" requires that sometime during their lifetime, they had not been individually chosen.
Thus 1 Peter 2:9-10 absolutely precludes anyone being chosen individually before creation. It is a lock no matter how much non-germane verbiage is posted.
When are our names written in the Lamb's book of life? When God chooses to credit our faith as righteousness and transfer us spiritually into Christ's spiritual body.
Is Salvation "conditioned" on the person's performance such that salvation is in part earned, merited, deserved, etc? Nope, so yet another deflection on display. Salvation depends on God alone. How many times must I say this in order for the taint so crowd to stop with their false charges? Seven times, or Seven times Seven?