If I install one will it affect the smog test (in CA). I've read that the pre-cat is only relevant for cold starts, so removing it shouldn't increase emissions on the test. And do the smog techs look for aftermarket equipment that isn't street legal? Do they care? Are they ignorant of the less common mods?

Most of the time people at emissions testing centers dont really care if your car is modded or not, just as long as it passes the tests. Sometimes they will say something but its rare and a lot of the times you can slip the techs a 20:)....but in CA i think you guys have more strick laws on modded cars. Visual or not. So i dont know, i highly doubt you'll have any problems, as i've heard various people from CA that have JDM engines have no problem passing, so i think your safe. You can always call an emissions place and ask too:)...that never hurts.