Mal 3:6 For I am the LORD, I change not; therefore ye sons of Jacob are
not consumed.
Not only does God's righteous character not change but God is also sovereign and therefore He is also capable of standing by His judgments and not changing those judgements. (i.e., Mal 3:6)
Yet because God is sovereign He has the ability to relent if He so chooses.
Let's look at an example from God's word that demonstrates this concept perfectly
(i.e., God can repent/relent but that doesn't mean He will in every circumstance)
God repented that He made Saul King....
1Samuel 15:10 Then came the word of the LORD unto Samuel, saying, 11 It repenteth me that I have set up Saul to be king: for he is turned back from following me, and hath not performed my commandments. And it grieved Samuel; and he cried unto the LORD all night.
Saul begs Samuel and asks that God pardon him.
1Samuel 15:24 And Saul said unto Samuel, I have sinned: for I have transgressed the commandment of the LORD, and thy words: because I feared the people, and obeyed their voice. 25 Now therefore, I pray thee, pardon my sin, and turn again with me, that I may worship the LORD.
But Samuel says... "nope!" God is not going to repent and pardon you.
1Samuel 15:29 And also the Strength of Israel will not lie nor repent: for he is not a man, that he should repent.
Then God affirms that He repented that He made Saul King.
1Samuel 15:35 And Samuel came no more to see Saul until the day of his death: nevertheless Samuel mourned for Saul: and the LORD repented that he had made Saul king over Israel.
God can and does change/repent/relent, but that doesn't mean He will in every circumstance.