Calvinist Bruce Ware talks about immutability:

Through much of the history of the church, God has also been understood as absolutely immutable in every respect. After all, it was often reasoned , if God can change, then that changeability must indicate a change for the better or a change for the worse. But if for the better, then he was not God before; and if for the worse, then he no longer can rightly be conceived as God.

Ware, Bruce (2008-05-15). Perspectives on the Doctrine of God (p. 90). B&H Publishing. Kindle Edition.