Changelings and changing

[Inevitability]

One of my players is playing a changeling. Nothing wrong with that, but I am wondering a few things.

1. Can a changeling turn into a half-dragon human?
2. Can a changeling turn into a werewolf in hybrid form? How about a werewolf in wolf form?
3. Can a changeling grow to large size by any means (say, the Enlarge spell), then turn into a Sahuagin Baron?
4. Can a changeling turn into a human currently under the effects of a Polymorph spell?

All help is appreciated.

[rollingForInit]

One of my players is playing a changeling. Nothing wrong with that, but I am wondering a few things.

1. Can a changeling turn into a half-dragon human?
2. Can a changeling turn into a werewolf in hybrid form? How about a werewolf in wolf form?
3. Can a changeling grow to large size by any means (say, the Enlarge spell), then turn into a Sahuagin Baron?
4. Can a changeling turn into a human currently under the effects of a Polymorph spell?

All help is appreciated.

I would say "no". I think RAI is clearly meant for it to just be a change to appearance, not abilities. So I'd allow someone to change into a werewolf in wolf form (if those are labelled as "humanoid") but I wouldn't give them any abilities. After all, all spells that allow you to change and take another creatures abilities explicitly state that you get their ability scores, powers, senses, etc ... And the shapechanger ability does not say that you get anything like that. It does not duplicate the effect of any spell, or it would have said so.

As for 4), I'd say that's clearly a "no". Why would it be able to do that? "Shapechanger" isn't a spell, and again it doesn't duplicate the effect of a spell. You might as well ask if you could shapechange into a human under the effects of Haste, Invisibility or Fly.

[Inevitability]

For clarity: I am only asking about change in appearance. For example, the werewolf in wolf form would look like a wolf, and it obviously increases a changeling's versatility if he can assume a form resembling a wolf (Seeing a human fire a crossbow at him would most likely cause a guard to attack back, but seeing a wolf fire a crossbow at him? Time to slowly back off.)

So let me rephrase my question: Can a changeling gain the appearance, but none of the abilities, of the aforementioned creatures?

[rollingForInit]

For clarity: I am only asking about change in appearance. For example, the werewolf in wolf form would look like a wolf, and it obviously increases a changeling's versatility if he can assume a form resembling a wolf (Seeing a human fire a crossbow at him would most likely cause a guard to attack back, but seeing a wolf fire a crossbow at him? Time to slowly back off.)

So let me rephrase my question: Can a changeling gain the appearance, but none of the abilities, of the aforementioned creatures?

Only for appearance I would say:

1) Yes.
2) Yes.

Those are basically just "races", in a way. There's no greater difference in terms of appearance alone between a changeling's true shape and a lycanthrope in werewolf guise or a half-dragon, than there is between the changeling's true shape and a dragonborn, half-orc or tiefling. Want to look like a Half-Dragon, Kuo-toa or a Bugbear? Sure! As long as you have seen one yourself in person.

3) Unsure about this. I'd probably go by Rule of Cool and allow it, but say that the spell ends you instantly revert back to your true shape instead, since the new form is too large.

4) No, since the shapechanging ability does not duplicate any spell. If you want to have the effects of a Polymorph spell (even just for the appearance) you have to have Polymorph cast on you.