The scientific version of the idea you put forth is known as the Many Worlds Interpretation of quantum mechanics. It is not a scientific theory, but merely an interpretation. It is a valid interpretation of the mathematics which does not contradict the reality we observe in any noticeable way. It's also slightly more nuanced, in that it deals with superpositions of worlds.
The mathematical version of this would require us to specify how many worlds there are and how many states there could be. It would also point out that there is no obligation of these universes being distributed uniformly. We may be an outlier, such that no world is quite like ours, or there may be infinitely many "clones" of our world.
The philosophical version would question what it means for a world to be identical to our own but for 1 change in the first place. Many philosophers would argue that "you" or "I" are unique, and thus any world with only one difference would suggest that you or I must not exist!
Applied mathematicians would suggest the question you are asking is with regard to the path invariance of our world. Does it matter how we got here, or only that we got here. Computer scientists might even bring up the concept of memorization to suggest how to implement a path invariant world time evolution efficiently.
So there's not just one way to look at this problem. Everyone will look at it a slightly different way. You get to decide where that leads you.