Undulating periodization just means to vary the intensity up and down a cyclic way — Hypertrophy / Strength / Power could easily be Low / Medium / High intensity. Or Low / High / Medium. And then you can validly mix them in different sequences. All that meets the definition of Undulating. But even though it meets that criteria, it will have different effects. Some will work better than others.
Back to your example — you can change the goal of one of the days to speed. It still meets the definition. But that’s no guarantee of anything. It may work, it may not. And I’m sure that’s the real point of focus for you. Based on your experience so far, if it seems like a good idea and like it would be worth a try, then give it a go and measure the results as best you can. I don’t have much intuition on it as I don’t coach in that environment. But I don’t want us to get hung up on categories so much that we lose sight of the goal. The category of Undulating Periodization is useful for teaching a concept. But in the real world, it’s almost always messier than that.