I really want to do this because I dig the signature Pontiac red and I'd love to have it in my Impala, is it possible? I was also thinking about swapping the stock Impala radio for the stock monsoon grand am one if it fits right.. Just to have the colors of the odometer and the radio matching. Please help me out here thanks!

I don't believe it has ever been attempted. Even if it was possible, you are looking at two different dash panels, different fitments, and that'* not even counting the electronic side of it.

I bet it would be easier to do a stock cluster modification to go for clearing the green, and putting down red, or even going with red LEDs. Also if you are looking in to the Monsoon system, I recommend going aftermarket at that point, because it can yield better audio results, with customize-able lighting colors.