I somewhat disagree with your post.
God never changes.
However men change, as does their understanding.
Mankind is born in sin.
He can not make his body become without having sin.
God covered Adams body of sin with an animal skin.
That clues me in, that SIN of an earthy man IS NOT REMOVED, but Covered.
When one recognizes blankets, animals skins, clothing, are physical things, covering a physical body, the satisfaction of the physical eyes, is their SIN is Covered.
However when we continue learning we find, Gods Covering of SIN, is not physical, but rather Spiritual. It is not with animal skins, blankets, clothing, but rather with the reflection of His Glory, His Light.
Sin is darkness, the absence of Light, the absence of God who is Light. Gods Light IS Supreme, the overpowers darkness, that it CAN NOT be SEEN. The darkness IS Covered By Gods Light.
When a man submits His Life to God, the man IS Giving God the Authority to Spiritually Enter the man, and Fill the man with the reflection of Gods Light, which Completely Covers the mans / Sin/Darkness.
God Bless,
Happy New Year,
SBC