I think alternative worlds is a valid subject for WorldBuilding, given its name. However, questions in the form of "What if we had exactly the same world we have today, except ________" where the blank is some new law of physics pose problems. I'd say at least half of them I have seen, if not more, are fundamentally broken in their understanding of physics to the point where asking for a physics based answer is like asking which cut of steak makes the best lemonade.
Others are simply ill researched. I am no expert on the topic of black holes, so I spent a mighty two minutes researching the topic on Wikipedia. A Schwartzchild black hole, by definition, has no charge. Electric charge cannot shrink the Schwartschild radius because if it has a charge, it is not a Schwartzchild black hole. Instead, you need to use the Reissner–Nordström metric, which works for charged black holes. This suggests either the author failed to research the topic in the least, or my two minute Wikipedia learning session was two wasted minutes.
I think there's room for well worded physics questions about alternate worlds. However, I personally get really nervous thinking about answers to physics based questions when it is clear the author asking the question is way over their head. Physics has this nasty tendency of declaring itself the authority on reality, unless you know enough to beat it back. I can easily see questions like that decreasing creativity, rather than increasing it. I like to give a lot of leeway to questions that inspire creativity, but I'm not a fan of those which go the other way.
If questions like these are fair game, as you recommend, I think they should be subject to a "homework rule," similar to that on Physics.SE or Mathematics.SE. If you come with a physics problem, you should also come with enough work done so that we can see where your understanding falls shy, and help with that part of the problem. Like on homework problems, its not the answer that is helpful, but the process. If the author had come in with "I want to add some fictional force to my world, which has an effect on charged black holes, but I don't understand the Reissner–Nordström metric, and how it might be manipulated by a disruptive force" we might be able to do something.
I do have to give this question credit for having a specific question. Many of the fill-in-the-blank physics questions are simply "what would happen if____". If there's any reason to reopen this question, its because it actually asked something specific enough to answer (which is clear because it was specific enough that I could note issues in terminology!).
Update:
Since I think this is an important metaquestion for WB to deal with, I've been giving it more thought since my answer. I realized recently that this question gives an excellent example where asking an apparently simple question about an apparently well defined new law yields dramatic unexpected results.
The author of the original question is clearly patterning the fictitious "species charge" after electromagnetism, with a minor change that opposites repel and like charges attract. Every single sentence in the question uses electromagnetic terms to describe what is going on, down to the point of suggesting using protons and electrons as example entities with charge.
From Columb's law: $F=k_e\frac{qQ}{r^2}$ where q and Q are the charges of two particles, and r is the distance between them ($k_e=\frac{1}{4\pi \epsilon_0}$, though I wont need that here). Clearly to get to the "species charge, we just negate that constant, yielding $F=-k_e\frac{qQ}{r^2}$. Simple right? Just like electrostatics, except now like charges attract.
However, it turns out this is the end of the similarity between electrostatics and this new force. The equations "look similar." However, the result of this is so completely and utterly unrelated to electrostatics in every way that I wouldn't even consider electrostatics to be template for how it behaves. In electrostatics, because like charges attract, there is a natural tendency for opposite charges to come together and act as a neutral charge. This effect is so pronounced that, even though gravity is immensely weaker than electrostatics by many orders of magnitude, gravity is still the dominating force in the universe. In this new fictitious force, nothing encourages its "species charge," as it was called, to neutralize. In fact, it would encourage the universe to rather rapidly divide into two halves hurtling away from each other incredibly fast. Thus, the universe will rapidly evolve into a state where you can effectively divide it in half and deal with each half-universe separately. Each half would be "similar" to our universe, only charged with like "species charges."
So how bad is this? From the original question, " This 'species force' between two electrons would be about 1,000 times less than the electric force between them - so it would be still far stronger than the gravitational force between them." Electrostatics is actually 39 orders of magnitude stronger than gravity, so that suggests this "species force" is 36 times stronger than gravity. Because nothing is encouraging cancellation, the result will be an attractive force that is immensely more powerful than gravity. Instead of finding ourselves pulled towards the earth at $9.8 m/s^2$, we would find ourselves accelerated at $9800000000000000000000000000000000000 m/s^2$! The resulting tidal forces would easily be enough to cause spaghetification, and the general collapse of the universe into two black holes. There would likely be no matter outside of the black holes.
Nothing in the question is concerned with the rest of the universe, but the rest of the universe literally got Bulldozed to support this "species charge." Whatever world was being built here is destroyed by its own forces. A single minus sign is the difference between the world we live in today, and a pair of supermassive blackholes containing all the matter in the known universe.
This is an example of why these questions are so tricky. There are so many unintended consequences to pay attention to when you decide to change the laws of physics.
