How can I convert a hair-particle system into 3D, editable objects? Is it possible to 'apply' a particle system so that it becomes workable 3d objects instead of being hair or emitter objects? If that's possible, then I should hypothetically be able to apply another hair-particle system to those objects, right?

I want to use this to make realistic feathers, if possible. The first hair system would be the shafts of the feathers, and the second would be the barbs.
In the modifier panel click the convert button.

 

That should do the trick.

Two things to note:


If you're using an object, the objects will be linked when converted.
The original emitter will continue to emit particles. Make sure to either delete the emitter, or delete the particle system.


By the way, CGCookie has a tutorial (archive) on creating a feather if you're interested.