It's not covered as far as I can see so I think it's a GM call. The above poster wouldn't allow it, I would as they have examples of the limbs possessing limited shapeshifting and call them out as functioning like a normal limb. So for me I'd let a shifter with one of these shapeshift as normal. Of course it would then have a red crystal wing/leg which would reduce its ability to hide as a normal animal but they get screwed over enough already in my opinion to lose such a core component of their design.