Sorry, I still don't understand your point.
Just a clarification of the law: All persons in the line of succession to the British throne are ostensibly Protestant, because the Act of Settlement restricts the British throne to Protestant "heirs of the body" of Sophia of Hanover:
[...] the Crown and Regall Government of the said Kingdoms of England France and Ireland and of the Dominions thereunto belonging with the Royall State and Dignity of the said Realms and all Honours Stiles Titles Regalities Prerogatives Powers Jurisdictions and Authorities to the same belonging and appertaining shall be remain and continue to the said most Excellent Princess Sophia and the Heirs of Her Body being Protestants [...]
The
former faith of a Protestant heir of the body only affects their right to the British throne if and when that former faith was Catholicism. A Catholic is barred "for ever" from succeeding to the British throne, even if they subsequently convert to Protestantism, by a clause in the Bill of Rights which is recited in the Act of Settlement:
That all and every person and persons that is are or shall be reconciled to or shall hold Communion with the See or Church of Rome or shall professe the Popish Religion F3... shall be excluded and be for ever uncapeable to inherit possesse or enjoy the Crowne and Government of this Realme and Ireland and the Dominions thereunto belonging or any part of the same or to have use or exercise any Regall Power Authoritie or Jurisdiction within the same
In contrast, should an "heir of the body" of Sophia be Orthodox Christian, Muslim, atheist, etc., they may convert to Protestantism and, if so, will thereafter be permitted to ascend the throne (provided, of course, that they have never been a Catholic).