Depends on the state.... and the strictness of the shop.
If you have an emissions test.... you might not pass. I don't know exactly how they test the cars.
IF you get an EXTERNAL wastegate then flat out it is emissions illegal, because your venting exhaust gas open atmosphere. But venting internaly and legally with cost you HP.
The place I took my car checked the brakes and then saw the intercooler and asked me to pop the hood. Then they put a sticker on my car. No questions asked. (and no-emissions testing in pa, yet. )