I'm wondering how Tiefling Heritages in Blood of Fiends interact with the alternate [sic] racial traits in the Advanced Race Guide.
Are the heritages sub-races or variants of the base race?
If they're variants (like an archetype for a class), then the Asura-Spawn's hideous laughter spell like ability has already swapped out the base Tiefling's darkness spell like ability and therefore Asura-Spawn are not eligible for Soul Seer (for example).
If they're a race in their own right, then they're eligible to swap out their spell like ability and fiendish sorcery for Soul Seer. Or indeed any other swaps the player wanted to make.