Good question and welcome to the forums Bers Erk! Of course most all cosmetic mods are legal except for really dark tint. As for engine mods though you'll want to be careful. Cali is notorious for being very strict as far as that goes. Pretty much anything that affects the cars smog certification is considered illegal.I just need advice on what mods are legal in California that I could add to my 2016 ecoboost.