I agree that there is no universal moral truth.

I heard once the story that Moses went down with the ten commandments and when he saw that the Isrealites worshipped a golden cow, he destroyed the stone tablets out of anger. Then he wrote down the ten commandments again, but slightly differently.

I don't know if that's true. He definitely destroyed the tablets once. It was surprisingly difficult to find the respective parts in the bible - I'm going to try again. The story might very well be not true!

The point is: Moral laws only matter if people know them and agree with them, so in the end what people think is the only thing that matters.

That's not the intentended meaning by the bible passages, they were probably just written by different people, or the author has forgotten what he has written the first time.

Edit: The relevant section is Exodus 34. God says that he will write the same words as on the first tablet. Then he goes on to state some commandments, which aren't the classical "10 commandments" but it's not clear to me which of them will go on the stone tablets or whether they are maybe just some additions that are not important enough to be written in stone.

The bible is not important to my point though - only subjective morals matter.