Respondendo para atualizar algumas informações nesta questão, o texto atual de Changeling não diz mais 'Humanoid'. Assim, parece que os Changelings podem agora tornar-se Esfoladores da Mente, Múmias, etc., embora sem nenhum dos seus poderes ou características especiais.
From Wayfarer's Guide to Eberron, DnD Beyond
Change Appearance: As an action you can transform your appearance or
revert to your natural form. You can't duplicate the appearance of a
creature you've never seen, and you revert to your natural form if you
die.
You decide what you look like, including your height, weight, facial
features, the sound of your voice, coloration, hair length, sex, and
any other distinguishing characteristics. You can make yourself appear
as a member of another race, though none of your game statistics
change. You also can't appear as a creature of a different size than
you, and your basic shape stays the same. If you're bipedal, you can't
use this trait to become quadrupedal, for instance. Your clothing and
other equipment don't change in appearance, size, or shape to match
your new form requiring you to keep a few extra outfits on hand to make the most compelling disguise possible.
Even to the most astute observers, your ruse is usually indiscernible. If you rouse suspicion, or if a wary creature suspects something is amiss, you have advantage on any Charisma (Deception) check you make to avoid detection.