Is reciting the Qur’an in the mosque, alternating between lengthened (with madd) and shortened (with qasr) pronunciations, contrary to the Sunnah of the Prophet?

There is no objection to reading the Madd Munfasil with a short (qasr) or medium (tawassut) length, and it is not obligatory for all readers to read with the same recitation as the first reader.