Ooooooh cause and effect interesting....! is the assumptions as follows: because a state cannot be observed by light that has not yet reached you, any faster than light alteration would nullify the light that has already left said item? Like, the stars are millions of light years away So some of them might not be here right now - but if you travelled to it via FTL and turned one of those dying stars green, the effect on that light already in transit that was not green, would then be in conflict hence why it would be time-travel?
So thought experiment:
Humanity has evolved without eyes. Light means nothing to us and we have no way of detecting it, but we were like bats creatures of echolocation... Would our opinion of the speed of sound be similar...? That going over 330m/s was basically moving outside of time, and if you could go faster than that you would have the same affects? But of sound we know that pressure waves weaken as they expand from their source/reflection and that new pressure waves smother and replace the old...? What of light waves? Do they interact? Can they cancel each other out can a dim white oppress and eradicate a dim green?
Also I'm wondering if you know: it is known light cannot accept extra speed by accelerating the source toward the receiver but can it be slowed down by accelerating the source away from the receiver? I know there is redshift but there is also blueshift. If light doesnt slow using the same experiment in reverse I would suspect the result for accelerating toward means something different to what we think it does...
I would step out from the observable single point of reference (a person's view) and put yourself in an omnipotent map view of the universe. Split it into a grid.
Each grid 'ticks over' based on its own local laws and independantly, and refreshes the local matter state each time. If an action e.g. "Planet exploder" was done from one region to an adjacent region faster than the speed of light, >between the ticks< a planet could be seen exploding as that region ticks over but you'd go... Why?? Then as the adjacent source ticks you'd see the gun fired.
It's easier to visualize the large flat map because scale really breaks the human brain, we just can't visualize the true scale & speed very well. The grid pattern is a falsehood of course, it's not nearly as uniform, gravity we think is more 'welly'
So to answer your question; it's not really based on a human perception as much as all of math's is foundationed on human perception. Think back to the ancient babalonians using feet & arms to measure then calculate area.
We can all agree that it's a bit of an oddity we take for granted, that our maths is applicable everywhere else - given that it's based off of our view. Mind blowing really. But "error carried forward" is something that really saved my butt plenty of times. You can still produce a right answer out of consistently incorrect original values, the answer will just be shifted by that error. When you consider math is linear and infinite on each end.... -3 -2 -1 0 1 2 3... It's not really a big deal, as long as it's all consistent.
Long story short; if bats could do math then their numbers may be very different than what we come up with. But theyd all be consistently different and exist in parallel to our calculations.
In regards to speeding up and slowing down light. No, light is a constant and doesnt change regardless of extreme or action.
What we perceive in regards to red shift is light being stretched out, the wave length doesn't lose energy (conservation of energy) it just takes up more spaaaaaaaace aaaaas itttttt thiiiiins ouuuut (this message is still the same but it has been stretched). By space, I don't really mean space - again a bit of a limitation of our language when simplifying a really complicated problem.
But from lights point of view; it's normal, everything else just got spaghetti-fied. But then again light doesn't have a point of view. So is it spaghetti or are we all spaghetti in this great big bowl of life?
And now we have left quantum mechanics and into string theory. So let's stop there before we all lose our minds... And also I have work :D