What if he decides to sell the car and wants to go back to stock? He's hooped.
What if he has to replace a light that's hardwired? He's hooped there too.
A proper adapter harness, using factory connectors, will enable him to swap lights without cutting, crimping or fuss. The proper HID connector at very least is needed to make that end weatherproof. The proper level connectors at the light and switch make it weatherproof and secure.