Airwalkrr, the main conceptual change is that Changelings are no longer actually fey. They are quite literally changelings; mortals who have been captured by fey at some point, and altered via fey magic, but who then escaped back into the mortal world. They still lead dual lives...for the most part only they can see each other's changed selves...but now they have the additional complication of having to be careful of attracting the attention of the True Fey again. During their time of captivity they learned to use faerie magic, which is expressed as "contracts" that enable some control over reality...though often with a reciprocal cost.