...owing to God’s free, NSD decision, he determined that he would relate himself to that which is other than himself—both the possible and the actual (this would include his eternal decree...). Then, he freely determined to bring about what he had determined would be actual, which itself was a subset of all that is/was possible. This is covenant condescension, and God takes on new properties in executing it; the Eimi, who himself is and always remains a se, takes on the eikon, in that he determines to relate himself to something(s) ad extra.
But this in no way sacrifices, undermines or negates who he is as the simple One-in-Three. He remains who he is, but he decides to be something else as well; he decides to be the God of the covenant. It was, to be sure, a monumental decision. It changed the mode of God’s existence for eternity; he began to exist according to relationships ad extra, which had not been the case before. But it in no way changed his essential character. Is this not the wonder of the gospel, from Genesis to Revelation?