def METHOD_NAME(tx):
    '''Modify the signature in vin 0 of the tx to fail CLTV
    Prepends -1 CLTV DROP in the scriptSig itself.
    TODO: test more ways that transactions using CLTV could be invalid (eg
    locktime requirements fail, sequence time requirements fail, etc).
    '''
    tx.vin[0].scriptSig = CScript([OP_1NEGATE, OP_CHECKLOCKTIMEVERIFY, OP_DROP] +
                                  list(CScript(tx.vin[0].scriptSig)))