A couple weekends ago I made the first appearance modification to my 2015 Subaru WRX STI. I threw on some Rally Armor Mudflaps. I was nervous after watching a few youtube videos of the install being done on older models which required you to remove the side skirts and pull back other parts of the body. Once I tore open the box and actually read the instructions though I realized it wouldn't be so bad.
I went slow with the install, triple reading the instructions and being very ginger with everything so it took me little over an hour. If I had to do it again, it would take me about half that time. For the front fender you literally remove 4 screws, pull some things back a bit, slide in the bracket, slide on the clips, and then put it back together. Then you mount hte flap to the bracket and you're done. The rear was even easier.
Here are some pictures for your viewing pleasure: