New Evo x MR. 100% stock. I realized that the front is higher than the back end especially on a full tank. Why is this so? Also can I change this without affecting ride quality and durability?

 

Yes, yes, and yes.

Stock height is slightly taller in front.
You can get aftermarket lowering springs that ride similar to stock. Swift springs for example
Yes they are designed to be compatible with the stock shocks.

 

Very nice might I say. I saw them on an evo x and its def a nice stance. Much lower. Does it effect ride quality? Although I know the ride is already slightly harsh stock. Also I really would like to not have underbody damage.

 

Under body damage from what? From the installation of the springs themselves and affect on the suspension? (tire wear mostly) Or from hitting things because the car is lower? If that, then yes, you'll have to be sensitive to the fact that the car is lower.