My main problem with this is the magic, I think changelings should be pretty good at an array of illusionary magic, and be able to learn one or two spells that are mostly dependent on their last(unicorn) disguise. I also think they should have some measure of hypnosis or mind magic that lets them get out of some tough 1 on 1 situations, maybe gives them an idea of how to act in certain situations.
oh, and telekinesis.
Secondary problem is that I don't think all common changelings need to look the same, some people might want their oc's to be pretty different, that should be left open.
My main concern is simple: The write up is way too long. It's very expertly written, so much so, that I think there's way too much. I don't think we can fairly expect a new player who wants to play a Changeling having to read this whole thing just to get an idea as to how the race works. The whole thing is a short story in of itself. There's probably a lot of it that could be made brief or cut altogether, rather than explaining anything and everyone anyone could ever want to know about changelings in one write up.
The Fun Has Been Doubled! is a My Little Pony: Friendship is Magic moderate-to-advanced forum roleplay. Set after the events of the fifth season, we currently have no overarching plot. Instead, we simply have created the world of Equestria for you as a giant playground to have fun in and to explore the magic of friendship. Canon characters and original characters are available for you to play as, both ponies and non-pony species alike! Just remember that we are account-per-character and we'll be fine!
So why don't you stay for a while, look around, and let us know if we should get a welcome party started for you.