No. Royal prerogative is only exercised on advice of the prime minister, the cabinet or by the consent of parliament. Constitutional convention is not just tradition. And the fact that the constitution of the UK is uncodified doesn't mean the monarch has any de jure powers. Even the prorogation of parliament on advice of the prime minister was held to be unlawful: https://en.wikipedia.org/wiki/R_(Miller)_v_The_Prime_Ministe...