I saw a Legendary Bos and she has a Chameleon chest piece I want. Is there a way to kill her without getting in trouble? I have zero chance of stealing it, so that's out for now.

As long as there is no named BoS members around, you can kill any BoS member you want. Even if they were to go hostile on the Pwedyn, just sleep for 24 hours and they should reset.

Have Danse with you after Blind Betrayal. All BoS members will go hostile, kill them and loot their body. Once you dismiss Danse, all BoS members will go back to normal, provided you didn't kill any named members. You don't even have to wait 24 hours with Danse.