could God have made morality different? If the answer is yes, then it shows morality is subjective because it could have been different. If no, then why not?
The best way to answer this question is to define morality properly. This is a variation on the question “is something good because God declares it to be good or is something good because it is good in itself.”
This is a question that cuts to the ontology (being) of good but I would argue that if we accept the premise that good is something independent of God then we don’t run into any issues down the line.
I would argue that goodness, like logic, finds its ultimate root in God’s character. That is, the way we know goodness is by understanding God’s being.
So the question of whether God could have made morality different could be rephrased like this: Could God exist in any other way than He currently exists?
If we understand God to be a necessary being who is unchangeable and whom exists in all possible words (the definition of a necessary object/being) then the answer is no.
This question is also logically related to the question of whether God can create a rock so big He couldn’t move it. The answer of “no” is not because of some limitation in God but because of the necessity of God and what flows from His being. In the case of the rock that would be logic. Its a logical category fallacy to assert that God could create a rock that retains its physical dimensions so as to be considered a rock while equaling a metaphysical being.
The same can be said for morality. It cannot be any other way than it is because it finds its definition and meaning in the being/character of God. And as a necessary being, God could not exist in any other form than His current one.