E.g. this question is there a good tag to indicate changing some single thing about real-world physics as the basis of a story? That's not normally what we mean by an alternate universe. It's a common SF technique, and I think something common that comes up here.
Worldbuilding is not What-if site
See this discussion: In past, the community agreed that Worldbuilding is not what-if site and most what-if questions fall outside the scope of Worldbuilding.
The linked question is to me example of the most part I mentioned earlier.
My own idea is that we shoud not invent tags for changing one element in our universe, but rather close this kind of questions and link users to What-if site proposal
Changing the laws of the universe is a tremendously difficult thing for the worldbuilding community to help with. I've fielded several of these questions, and in general the answer to "What if the universe was exactly like ours except for ________ rule" is "The universe would be completely and utterly unrelated to everything you can imagine."
The problem with such science based questions is that changing a small rule of the cosmos can have extraordinary consequences. Typically these consequences are far beyond anything the original question author considered, or sometimes well beyond their mathematical capacity.
They're also really hard because it takes 10 seconds with Wikipedia to formulate such a question, and it can take far longer to answer. Some questions may requires months of a PhD's time to refute, and then 30 seconds later there's a new one.
A while back I started proposing that questions in that form be treated like homework problems on other stack exchanges. Our job would not be to give them the answer, but to take their work, find out what they did [wrong], and help them explore new avenues where creativity might flourish. It would make such questions about the method, not the final answer.
Worth noting your meta post title isn't exactly the same thing as the question you linked. In the question they just want to explore a world where a measurable quantity is different. That kind of question may also be in this crazy realm where the unexpected is around every turn, but it has a general tendency to be more benign. The nasty questions are the ones where we try to change a law of physics like "What if oxygen wasn't attracted to carbon? How would that change aquatic life." (Answer: it would be completely and utterly unrelated to everything you can imagine. For starters, that would prevent metabolism by the Kreb's cycle, so literally every aspect of every living creature would have to change).