And
God saw their works, that they turned from their evil way; and
God repented of the evil, that he had said that he would do unto them; and he did it not.
Jonah 3:10 KJV
Jonah 3:10 KJV shows that
>turning from sin is works (eph 2:8-9, Romans 3:28, 4:6, Titus 3:5)
>God repents
As for Numbers, when it says "God is not a man that he should lie, nor repent," it is saying that God does not change his mind about his promises to his people. That is the context. It's not saying he never repents (changes his mind). He changed his mind about what he would do to Nineveh. What he doesn't change his mind about is his promises:
"God is not a man, that he should lie; neither the son of man, that he should repent: hath he said, and shall he not do it? or hath he spoken, and shall he not make it good? Behold, I have received commandment to bless: and he hath blessed; and I cannot reverse it" (Numbers 23:19-20).
This is surely a marvellous declaration. It tells us that once God enters into an unconditional covenant with any people He will never call back His words.
We see this also in God's eternal security, that he will not change his mind about what he has given us:
For the gifts and calling of God are
without repentance.
Romans 11:29 KJV
God's peace be with you