Interesting question! Short answer: sometimes.

Here's the long answer. I think that the words "magnification and "refraction" should be switched in your question. That's because every material has a property called the refractive index. On the other hand, you can change the magnification of a telescope in many ways, like by changing the refractive index of a lens, or by cutting the lens into a more curved shape, or by moving the lens up or down the telescope.

How does the refractive index affect magnification? The refractive index n determines the angle of refraction for light that enters a new medium. In other words, the refractive index controls how much light "bends" when it passes through a new medium. Here, "medium" means any substance or material that light is passing through, whether it's solid, liquid, gas, or a combination of different things. For example, the medium can be air, water, glass, a rain-cloud, or simply vacuum (nothing). Each of these media has a different refractive index.

Snell's law tells you how light will bend when it changes media. Wolfram ScienceWorld has a simple diagram showing how Snell's law works. You need to know three things: the refractive indices for the starting medium (n₁) and the end medium (n₂) and the angle of incidence (the direction that light is coming from). Then you can use Snell's law to calculate the angle of refraction.

So does the consistency of a medium change its refractive index? Sometimes. Let's just say that every medium can have a different refractive index. For example, a dense glass usually has a much higher refractive index than a light glass. For other materials, I don't know any rules about how consistency will affect the refractive index, or if it would have no effect--I would just have to test it.