I am bringing my Scion TC in for a routine maintenance check in a few days, and I have just had a pair of 8000k HID headlights installed. Will Toyota tell me to remove them when they see them under the hood?
They won't tell you to remove them. They might point out that you voided the warranty on your electrical system. HIDs are illegal in the US if the car didn't come factory equipped with them so if you will need an inspection to renew your registration you will probably be forced to remove them then.