Can cars bought in Hong Kong be taken to Thailand for use?

This is not impossible, but you must have a driver's license from Chinese mainland, Viet Nam, Laos and Thailand at the same time.

To buy a car from Hong Kong to Thailand, first drive to Huanggang Port, enter Shenzhen, then pass through Dongguan, Zhongshan, Jiangmen, Kaiping, Enping, Yangjiang, Maoming and Huazhou in Guangdong, turn to Beibu Gulf, turn to Nanning, turn to provincial highway 325 via Nanyou Expressway, and then turn to provincial highway 2 19 to reach the Sino-Vietnamese border.

Then it passes through Vietnam, Laos and finally Thailand.