Your challenge, would you choose to accept it, is to prevent Qin to defeat all six states to form the first Chinese empire in our history, with a POD no earlier than 265 BC. That means I would accept ideas that justifiably prevent Qin's victory in the Battle of Changping, or that the assassination attempt on Qin Shi Huang succeeded. Bonus if China could remain divided, and the written language and measuring units of the seven states could be kept for another 200 years. Double bonus if a state other than Qin united China at last. Triple bonus if, instead of a unification, all seven states developed strong individual identities, and at least 3 of them remain divided until present day, though their expansion into other parts of Asia and present day China would not be restricted.