If you gain a Changeling to your hand via Artisan or Transmogrify, can you choose to exchange it for a Changeling from the supply (which would then go in your discard pile)?
It seems like you can, reading the Exchange rules carefully...
The card being exchanged is returned to its Supply pile, or non-Supply pile, and the card being exchanged for is taken and put into the player's discard pile. This does not count as gaining a card. The exchange only happens if both cards can be exchanged; if the pile is empty, the cards are not exchanged.
So in order, you put the Changeling you just gained back in its Supply pile, and then you can take a Changeling (which happens to be the same one you just put back).
Very rare that you would want to do this, but you might need that card in your discard pile instead of your hand for something.
Bonus question: if you can do it, can you still do it if you just gained the last Changeling; making the pile empty? Again the pile will become non-empty when you return the card... or does the card have to be there before you begin the exchange?