Using the mannequin as a placeholder

I went through the videos for the animation and rigging tools, and one thing that was glossed over that I’m interested in is being able to customize the mannequin and using it to make your animations as a placeholder. Can someone detail, or point me in the direction of where to find out, this aspect a little more? More specifically, when you have your actual mesh made, how do you replace the mannequin, keeping all the previous animation and skin weighting, etc?