I don't know of anything that lets you actually swap body parts in Poser. You might be able to rig something together by hiding body parts, like some of those centaur figures are made.

For a cheaper alternative to Creature Creator, check out the Creature Creation Pack at DAZ. It has wings, tails, horns, etc., that you can attach to your figure.

And it is possible to swap heads, by hacking the CR2.

What exactly are you trying to do? Maybe someone has already done it.