does adding a sight to any gun ever actually change how the sight looks?
I don't think so. Every gun uses the same exact sight. The only thing I can think of is the Bipods. They change across weapons, one example is the bipod on the PKP Pecheneg. It has a different appearnence than the one on the M60 or M240.
So to answer TC's question, I don't think the MARS sight will appear. You could just try to use the American holographic sight on it and pretend it is. Looks nearly the same.