We may be talking about two different things. I'm talking about a multiverse where different parts have different values for constants (like the fine structure

We may be talking about two different things. I'm talking about a multiverse where different parts have different values for constants (like the fine structure or gravitational constant) but the equations are the same. If you're talking about a universe with structurally different equations implying different conservation laws, then indeed we can't demonstrate anything about it.