I would say yes, since 50% of both parents' genetics goes into the child, though the child may bare more resemblance to one more than the other. If you look at changelings and ponies, they are both clearly equine, so mating should theoretically be plausible. It is about the same with all the races of us--humans! If you have a mixed racial pair (ex. caucasian x african) the child borne is usually mixed race, bearing traits of both races. If we assume that holds true for ponies, we would want to mix the changeling features with the pony features to make something of a blend of both, with one parents' genetic traits a little stronger than the other's due to dominant genes. If we think of it that way, we want to mix the most prominant features. Let's consider an earth pony x changeling cross. The child, we would want to give holey legs, perhaps a stunted holey horn or beginning of one like a bump on the forehead, and maybe or maybe not some feeble buggish wings that may be useless for flying capability. The child may or may not be able to use magic to change its appearance for shortened periods of time, and it would (beginning the more earth ponyish half of its genetic line) be stronger and fast despite its feeble looking frame. It would also bear the bright colors of the parent earth pony, though perhaps darkened to a muddier tone because of the mostly blackish frame for its body, with stripes of bright color in the mane and tail mixed between the parents' mane and tail colors.
Of course there are numerous combinations that could genetically occur, perhaps meaning the legs would be solid and not holey at all, while the horn and wings are retained but perhaps not at all or fully usable and look to be so. My biggest problem in thinking about this is the body chemistry itself though--the holey legs, because I feel like they wouldn't support a heavy mammalian body, which I'd assume is a dominant trait for ponies that aren't pegasi.