> Keep in mind that anything is possible if the Cosmological Principle turns out to be false, and if we can travel far enough to escape our local zone.
This is... overly optimistic. To say the least, it depends on exactly which laws change with location, and how far. That is to say, we could conceivably know for a fact that the Cosmological Principle is false, but still know that there is nowhere in the universe that time travel is possible, or that it's impossible to prevent the end of the universe. The only way "everything is possible" is in the conditional sense that we don't know what's possible yet, but you don't need to invoke the CP for that at all.
This is... overly optimistic. To say the least, it depends on exactly which laws change with location, and how far. That is to say, we could conceivably know for a fact that the Cosmological Principle is false, but still know that there is nowhere in the universe that time travel is possible, or that it's impossible to prevent the end of the universe. The only way "everything is possible" is in the conditional sense that we don't know what's possible yet, but you don't need to invoke the CP for that at all.