There will be no changing back and forth.... Twinkling of an eye is certainly not GRADUAL
1Th 4:16 For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:
1Th 4:17 Then we which are alive [and] remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
Those that are alive will already be changed before caught up to meet the Lord. Natural mortal bodies will not endure without a change.
Everyone has their own interpretation of Rapture. Of course no one could possibly be mistaken. Most everyone agrees that there will be one.