I think it's quite reasonable to reserve the designation of 'core Amarrian belief' to beliefs that are at least
shared by all Amarr that aren't heretics or apostates.
Even for royalty it's not at all clear that the 'not having clones' belief is directly following from Scripture, by the way: It is following from the Sacred Flesh
doctrine which says directly that the flesh of royalty is sacred. The restriction against the cloning of any member of a royal family is not part of the doctrine itself
, but taken to be a consequence
of the doctrine.
So, it might be a belief found amongst Amarr that Amarr generally ought not have clones: But that's far from being a core Amarrian belief
, which really implies that it's universally held amongst Amarr. And not only that, but furthermore that it is a belief at the core of the beliefs shared by all Amarr, which indicates that other beliefs are derived from it, rather than the other way around. It is arguably neither.