Why this works:
From rule 706.2: "The “copiable values” are the values derived from the text printed on the object (that text being name, mana cost, color indicator, card type, subtype, supertype, rules text, power, toughness, and/or loyalty), as modified by other copy effects, by its face-down status, and by “as . . . enters the battlefield” and “as . . . is turned face up” abilities that set power and toughness (and may also set additional characteristics)." (emphasis added)
Changeling is part of the rules text and is thus copied, giving your Jwari Shapeshifter Changeling as well.