If your Changeling has Glamours, then masking your non-human features seems like a pretty basic use of a Seeming. In fact, not only can you mask these features, but you can disguise yourself as another too. I love the Glamours power, and I personally think that it's more fitting for a Changeling than Human Guise. Why? Because I like that a Changeling has to exert at least a minimum of supernatural effort to look human, whereas Human Guise makes you look human until you exert supernatural effort.