If you need to access the parameter inside of a material that is set by the material, then you can use the same method as I mentioned. You will have to use blueprint as an intermediate to change or get the values of a material (A dynamic material). Alternatively you can use shader code, vectors and camera features to calculate such things within the shader. Depending on the complexity a full shader solution would work as well.
You can also use something called Material Parameter Collections | Unreal Engine 4.27 Documentation