Totally nitpicking here, but since we're on the topic: it always irked me that the skin-spies have a set of teeth beneath their face, implying those stay the same while the face changes. I get why it was done (a. teeth would I guess be hard to change quickly, and b. the imagery of just teeth and eyes beneath the "fake" face is great), but it still jumps out at me when I'm reading.
I mean, what if they had to impersonate someone with bad teeth? Maybe dental hygiene is just great in Earwa.
Also hair. How does hair work? Does it change color and length? Does it all fall out and new hair grows? If so, what happens to old hair? Do they at least donate it?
Screw Meppa's identity -- these are the questions that need answering.