| Ambassador |
Specific trumps general if it explicitly says so, or directly contradicts the general rule.
The entry for the Lyrakien says : "A chaotic good 7th-level spellcaster
can gain a lyrakien as a familiar if she has
the Improved Familiar feat."
The entry for the Arbiter (same Bestiary 2) says : "An arbiter inevitable can serve a spellcaster as a familiar.
Such a spellcaster must be lawful neutral, must be at least
caster level 7th, and must have the Improved Familiar
feat."
One of them explicitly says that a spellcaster "must" be LN. This is a case of the specific trumping the general, since the supplementary condition is explicit.
The Lyrakien entry is not worded the same way and does not contradict the general (feat) rule. In fact, several other entries in the Bestiary 2 are worded like the Lyrakien's.