They don’t have to make any declarations to not believe in a mishugas. You just don’t have to believe.
But for your information, look at this statement:
A 1996 statement from Agudas Chasidei Chabad said:
With regard to some recent statements and declarations by individuals and groups concerning the matter of Moshiach and the Lubavitcher Rebbe, Rabbi Menachem M. Schneerson, of sainted memory, let it be known that the views expressed in these notices are in no way a reflection of the movement’s position. While we do not intend to preclude expressions of individual opinion, they are, in fact, misleading and a grave offense to the dignity and expressed desires of the Rebbe. The statement reads that “The Rebbe clearly inspired a heightened consciousness of Moshiach, one of Judaism’s principles of faith, and towards this end, encouraged the study of the traditional sources concerning belief in Moshiach, the Redemption and its imminent fulfillment, as well as an increase in activities of goodness and kindness. This should be perpetuated by all, as we strive for a more perfect world and the fulfillment of the Rebbe’s vision.
It continues:
Unfortunately, the Rebbe’s words are now being distorted and quoted out of context by a numbered few. This reckless behavior, even if well intentioned, is antithetical in the extreme to all that Lubavitch represents as defined by the Rebbe. The Rebbe explicitly and emphatically advocated a thoughtful, respectful and responsible approach in this and related matters, and resolutely opposed such distorted pronouncements time after time, both publicly and privately.[88]
A statement from Vaad Rabonei Lubavitch said:
A 1996 statement from Agudas Chasidei Chabad said:
With regard to some recent statements and declarations by individuals and groups concerning the matter of Moshiach and the Lubavitcher Rebbe, Rabbi Menachem M. Schneerson, of sainted memory, let it be known that the views expressed in these notices are in no way a reflection of the movement’s position. While we do not intend to preclude expressions of individual opinion, they are, in fact, misleading and a grave offense to the dignity and expressed desires of the Rebbe. The statement reads that “The Rebbe clearly inspired a heightened consciousness of Moshiach, one of Judaism’s principles of faith, and towards this end, encouraged the study of the traditional sources concerning belief in Moshiach, the Redemption and its imminent fulfillment, as well as an increase in activities of goodness and kindness. This should be perpetuated by all, as we strive for a more perfect world and the fulfillment of the Rebbe’s vision.
It continues:
Unfortunately, the Rebbe’s words are now being distorted and quoted out of context by a numbered few. This reckless behavior, even if well intentioned, is antithetical in the extreme to all that Lubavitch represents as defined by the Rebbe. The Rebbe explicitly and emphatically advocated a thoughtful, respectful and responsible approach in this and related matters, and resolutely opposed such distorted pronouncements time after time, both publicly and privately.[88]
A statement from Vaad Rabonei Lubavitch said:
Belief in the coming of Moshiach and awaiting his imminent arrival is a basic tenet of the Jewish faith. It is clear, however, that conjecture as to the possible identity of Moshiach is not part of the basic tenet of Judaism. The preoccupation with identifying the Rebbe (zatza”l) as Moshiach is clearly contrary to the Rebbe’s wishes. Together with the whole of Klal Yisrael we pray for the fulfillment of our collective yearning for Moshiach, in the spirit of the timeless Jewish declaration: “I await his (Moshiach’s) coming each and every day”. – wikipedia, translated from kol koreh chabad.