"More changeful" implies constant, frequent change. The antonyms for this phrase would then be terms that describe consistency and stability. Some possible antonyms for "more changeful" include constant, uniform, unchanging, settled, steady, and even. These words all suggest a state of being that is predictable and unwavering, rather than one that is characterized by shifting and flux. Alternatively, other antonyms for "more changeful" might include inflexible, fixed, or stagnant, which describe a lack of movement or alteration over time. Ultimately, the choice of antonym will depend on the context in which "more changeful" is used and the effect that the writer or speaker wants to convey.