There is a pillar in the ground, and a horse walking by.
The horse is first on the left. But then, the pillar is on the left of the horse. Did the pillar change?
Creation changed with relationship to God at the Incarnation, but God does not and cannot change with relation to anything. Once you jump the gap, in fact, into these kinds of discussions, we would say that strictly speaking, “relation” is something creation has with God, but that God does not have with creation. That is difficult to understand, as it is not able to be reconciled with the common usage of the word in preaching and teaching.
Put another way, it is the flesh that is being changed, in the instant of its creation, to be united to the Divine Person of the Son… God does not need to change for this to happen. His will and intellect remain as they are, but the human body and soul have conformed to it as they come into being.
A more basic question is, “How can God will anything? That would seem to imply a change.” But this misses the transcendence of God - He does not deliberate, and His will is simply convertible with reality… there is no “intermediate” step that would involve change.