I added a black valance to my 2016 SR5 and it wasn't too difficult. I had originally planned to do it without taking the front bumper off by
following this guide.
I eventually decided to just remove the bumper and use a dremel to cut the slots to clip the valance in place. It was super easy because the slots to cut were already marked on the inside of the bumper. I used
these clips to install the valance. Amazon says they don't fit but they definitely do.
The bumper removal video that helped me the most was
this one.
I know you can get an unpainted valance fairly cheap but I just bought the genuine Toyota TRD Pro valance on eBay for a little over $200.
Good luck!