Changelings don't copy traits

[Roomba]

The trait that allows you to see other people's traits costs very little and can be picked up practically for free. I don't think it's as conditional as you make it out to be - all you need to do is to have seen the ling once, and from then on you can call them out whenever they enter viewing distance. Memorizing the traits of one guy isn't the monumental feat of memory it's made out to be.

I dunno, I'm partial to having the ling flat out copy the traits of whoever they're taking the form of, like mutations. If you want to take on another person's identity, that means committing yourself to both their strengths and their weaknesses.