Can you endorse a check as not used for purpose intended?

Endorsing a check 'not used for purpose intended' makes little sense. While you can endorse a cashier's check or money order 'not used for purpose intended' this is only because these are financial instruments backed by cash. A check, on the other hand, represents the promise of available funds in an account, to be provided to the payee upon demand. There is no guarantee that a check won't bounce. A cashier's check or money order has been paid for up front, and cannot bounce. This is why you can endorse a cashier's check or money order 'not used for purpose intended' while you cannot do the same for a check.