God does not change. God never changes his mind. God is omniscient. The word of God is the word of God from the beginning of time until the end of time.
"17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil. 18 Yes indeed! I tell you that until heaven and earth pass away, not so much as a yud ( י ) or a stroke will pass from the Torah — not until everything that must happen has happened. 18 "For truly I say to you, until heaven and earth pass away, not the smallest letter or stroke shall pass from the Law until all is accomplished. 18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled. 19 So whoever disobeys the least of these mitzvot and teaches others to do so will be called the least in the Kingdom of Heaven. But whoever obeys them and so teaches will be called great in the Kingdom of Heaven. 19 "Whoever then annuls one of the least of these commandments, and teaches others to do the same, shall be called least in the kingdom of heaven; but whoever keeps and teaches them, he shall be called great in the kingdom of heaven. 19 Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven."
God’s intrinsic nature cannot change, but He can certainly deal with sin as He sees fit, and under the new covenant, He sees fit to forgive it because the price was paid by Jesus.