I'll bet that there are plenty of astrophysysicists who are mathematicians who could calculate a very different distance by calculating a gradual change in math and physics into it. But why do this when it is so much easier to use all kinds of constants that we don't for-a-fact know existed more than a million years ago?
I'll concede that scientific understanding of the distant past is a projection, and that the universe changes over time. You're not talking differences of degree though, about whether the universe is 10 or 15 billion years old - you're saying (in the religion thread) a few thousand or (here) a million, which is simply not true. That can and has been easily tested right here on Earth. Isotope analysis such as radio-carbon dating has proven far beyond reasonable doubt that the Earth is over 4 billion years old.