In an article by John Piper, he cites Psalms 110:4 as a prooftext of God not being able to repent:
Psa 110:4 The LORD has sworn and will not change his mind, “You are a priest forever after the order of Melchizedek.”
This is one of the strangest prooftexts used by Calvinists to defend the idea that God cannot change. Within the very verse, unique conditions are described. God is saying He will not repent because He has sworn. God did not swear everything about everything, but only a specific promise (“an eternal priesthood”). Literally, Piper’s prooftext that God cannot change His mind is a text that describes one thing that God is committed to accomplishing. The natural suggestion is that God has latitude to repent on things about which He has not made such pressing promises. Piper’s prooftext cannot be generalized and is evidence against Piper’s own position.