Christianity addresses this supposed paradox by admitting that the final answer is beyond our human limits, that God manifests in three ways which we Christians believe is the triune nature of God. God may have many more 'unes' but we have evidence of three: God the Creator Who IS and thus IS before and after all that there is + God the Holy Spirit Who sustains the balance which is so delicately posed to keep the universe capable of bringing forth life + God The Son as Jesus The Word Who took flesh and dwelt among us.
In the Christian conceptualization of The Trinity, God The Creator is not diminshed when God The Holy Spirit sustains the entire of the universe, nor is God diminished when The OWrd become flesh and dwells among us. In fact we use an analogy to simplify this non-dimishing nature of the Triune God: when you love, you are not diminished by giving that love (in agape or eros or filia).
The problem is not merely that the creator changed after an act, but that the creator was never free from the bondage of time, in the first place. A change of state required to perform something at a finite moment renders the performer chained to the influence of time, both before and after the act was performed. Otherwise, change would not be possible. No change implies no finite moment of creation.