The custom of Dragon Boat Festival is not one of the traditional festivals in China, but eating zongzi, rowing dragon boats, climbing the moon and inserting mugwort leaves.

A. Burning incense in front of Tomb-Sweeping Day's tomb is a chemical change, so the choice is wrong;

B, climb the Double Ninth Festival, overlooking Cornus officinalis, no new substances are generated, which is not a chemical change, and the options are correct;

C. Eating zongzi and burning mugwort leaves during the Dragon Boat Festival is a chemical change, and the option is wrong;

D every household will set off firecrackers during the spring festival. Setting off firecrackers is a chemical change, so the option is wrong;

So choose B.