No longer a Bahá'í? You can't serve on an LSA, but you can still aspire to be declared a Covenant-breaker.
In Islam, apostasy is considered a crime against the Faith, and in the past was commonly punsihable by death.
Those who turn back as apostates after Guidance was clearly shown to them, the Evil One has instigated them and busied them up with false hopes.
Qur'án 47:25
Though Bahá'u'lláh never said anything to turn away from this Islamic principle, Bahá'ís don't regard apostasy as a serious offense. However, if an apostate is relentless enough in his opposition to the Bahá'í Faith, he can then be regarded a covenant-breaker, which is typically defined as a Bahá'í who turns against the present Bahá'í leadership, but a covenant-breaker need not be a Bahá'í:
People who have withdrawn from the Cause because they no longer feel that they can support its Teachings and Institutions sincerely, are not Covenant-breakers — they are non-Bahá'ís and should just be treated as such. Only those who ally themselves actively with known enemies of the Faith who are Covenant-breakers, and who attack the Faith in the same spirit as these people, can be considered, themselves, to be Covenant-breakers.
From a letter dated March 30, 1957 on behalf of Shoghi Effendi, "Messages to Canada," p. 64
Hence belief in Bahá'u'lláh is not a prerequisite for Covenant-breaker status. The only prerequisite is that one is or once was a believer. Once more:
Following the successive blows which fell with dramatic swiftness two years ago upon the ring-leaders of the fast dwindling band of old Covenant-breakers at the World Center of the Faith, God's avenging hand struck down in the last two months, Avarih, Fareed and Falah, within the cradle of the Faith, North America and Turkey, who demonstrated varying degrees, in the course of over thirty years, of faithlessness to `Abdu'l-Bahá.
The first of the above named will be condemned by posterity as being the most shameless, vicious, relentless apostate in the annals of the Faith, who, through ceaseless vitriolic attacks in recorded voluminous writings and close alliance with its traditional enemies, assiduously schemed to blacken its name and subvert the foundations of its institutions.
Shoghi Effendi, Messages To The Bahá'í World: 1950-1957, pages 53-54
Shoghi Effendi often spoke of apostasy of as though it is an evil in and of itself:
Some have apostatized from its principles, and betrayed ignominiously its cause.
World Order, page 195
He who had been instrumental in inaugurating so splendid an era in the history of the Faith, on whom the Center of Bahá'u'lláh's Covenant had conferred the titles of "Bahá's Peter," of the "Shepherd of God's Flocks," of the "Conqueror of America," upon whom had been bestowed the unique privilege of helping `Abdu'l-Bahá lay the foundation-stone of the Bab's Mausoleum on Mt. Carmel—such a man, blinded by his extraordinary success and aspiring after an uncontrolled domination over the beliefs and activities of his fellow-disciples, insolently raised the standard of revolt. Seceding from `Abdu'l-Bahá and allying himself with the Arch-Enemy of the Faith of God, this deluded apostate sought, by perverting the teachings and directing a campaign of unrelenting vilification against the person of `Abdu'l-Bahá, to undermine the faith of those believers whom he had during no less than eight years, so strenuously toiled to convert.
World Order, page 82-83
The volumes which a shameless apostate composed and disseminated, during that same period in Persia, in his brazen efforts not only to disrupt that Order but to undermine the very Faith which had conceived it,...
God Passes By, page 327.
Apostates, rebels, betrayers, heretics, had exerted their utmost endeavors, privily or openly, to sap the loyalty of the followers of that Faith, to split their ranks or assault their institutions.
God Passes By, page 408.