Ok let me ask you this.
In Rev 6:9
And when he had opened the fifth seal, I saw under the altar the souls of them that were slain for the word of God, and for the testimony which they held.
Who are these people?
And are they different form 1 Thes 4:15?
For the Lord himself shall come down from heaven with commandment, and with the voice of an Archangel, and with the trumpet of God: and the dead, who are in Christ, shall rise first.
Are they the same or different groups of people?
That is a figurative statement. It represents all currently in Paradise covered by the Atonement.
All of the redeemed. They have permanent incorruptible physical bodies. At this point they are glorified. The spirit is put on over the physical body like a robe of white.
The 5th and 6th Seal happen at the same time. This is John's version of Paul's Second Coming/rapture event found in 1 Corinthians 15 and 1 Thessalonians 4.
Those on earth put on a permanent incorruptible physical body and the whole church puts on the spirit like a robe of white. The church is presented to God and is forever with Adonai God in Paradise until the New Jerusalem descends after the Millennium.
Jesus then proceeds to the Mt. Of Olives and prevents an attack per Zechariah 14. Then the 7th Seal is opened. Then Israel is dealt with during the first 6 Trumpets. Jesus is sitting on His throne in Jerusalem per Matthew 25:31. Jesus starts removing people from the Lamb's book of life. The goats are the first to be removed. This is the final harvest, and the time of Jacob's trouble, or the GT.
So your verse about all not being changed is taking the verse out of context for the church and applying it directly to Jacob/Israel. Some of Israel are sheep and remain in the Lamb's book of life, and live on earth for the 1,000 years. The goats are not changed. They are sent to the LOF, and their names removed from the Lamb's book of life.
After the 6 Trumpets, we see in Revelation 10 the 7 Thunders. This is Jesus dealing directly with the Nations after Israel is harvested. Matthew 13 covers this harvest, while Jesus and the angels are on the earth. The wheat is changed and many souls enter the Millennium. The tares are placed in the LOF, not changed. Their names removed from the Lamb's book of life. After the 7 Thunders, we have the final celebration week of the 7th Trumpet. This week is one of 3 historical weeks depicting a dispensational change.
The first celebration week was when Israel took over Jericho, ending the Nations and setting up Israel as the number one Nation. That did not go as planned. Israel was just as wicked as the rest of the world. The next week of celebration was the week of the Cross. Israel was set aside and God started the NT church. This was called the fullness of the Gentiles.
Now at the end of the church, we see the church removed first. The first will be last and the last will be first. Then Israel will be harvested in preparation for the Millennial Kingdom. Then the Nations will be harvested. Then the third week of celebration to present the Kingdoms of earth as belonging fully to Jesus as Prince. Jesus will rule until all is fulfilled, and then hands the Kingdom back to God.
Back to the 7th Trumpet. If an interruption is necessary, there will be 42 more months of utter desolation to allow those who will be beheaded to remain in the Lamb's book of life. This is the gleanings after the final harvest. And Satan will be allowed 100% control to do as he pleases on earth. Only those who chop their heads off to avoid the mark will remain in the Lamb's book of life and be resurrected on the first day of the Millennium. This is all spelled out in Revelation. If there is no 42 month extension, the 7th Trumpet will end and the Millennium will start. Jesus will still reign with the sheep, the wheat, and the 144k. These will continue to produce offspring per Isaiah 65. All those born during the Millennium will have one more chance like every one ever born on earth to reject Satan or be deceived by Satan.