Could some of the spies, near the top of the organization be facedancers/skindancers? The whole idea behind House Tleil'laxu (and the mention of selkie blood) was to have a medieval version of the Bene Tleilax.
Belief 1. There exist ruins with artifacts that I can use somehow to increase the dignity of the Traladarans and their ancient lines of leaders.
Sorry that I have been so quiet; I feels like a lot to digest
I just flipped through the Character Burner. I didn't see a doppelganger song.
It doesn't mean we can't burn up one... but it seems more akin to Sorcery or some Mannish magic. It's not really an "Elven" thing, in the Tolkienesque context of BW, since Elves are a purer expression of the "song of creation" - why change form when you are perfect?
So, options & ideas.
1) New Elven song. Break the context of Tolkien-style Elves.
2) Ditch the doppelgangers. Use Threne of the Chameleon instead, and say the Tleil'laxu are mostly uber-isolationist, stern Rangers... Borderline Dark Elves.
3) Use Fey-blooded Humans (Half Elves) with the Gift for the Facedancers.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.