Being able to make any change to the state of reality pretty much makes everything an meaningless endeavor. - Most Christians would say something slightly different - creation was unnecessary for God to do, which is different than it being meaningless. Since it was an unnecessary act, Christians usually say that creation itself is an act of Love, and therefore the meaning behind everything in creation is Love. For our part, the way CS Lewis described it is that the actions we take help shape our immortal soul, and so our actions derive meaning from this process aside from whatever happens in the material world. From this perspective, even if the universe "will just freeze into an eternal motionlessness" there is still meaning in what we do, for us and for God.
Since reality has meaning for God, it is not as far that goes dismissible that God would change reality. This is a different question from "Does God change reality?" It seems quite plausible that God could and would change reality but chooses not to. Different religious traditions (even within Christianity) have different opinions on this.