This is the first test for my idea of the LiveMorph clothing system.
The Material and Shape keys that constitute the change are both controlled by drivers that are triggered by the small bone you see in front of the model in the Gl model.
The idea is to have several complete outfits contained within the same mesh, but this is obviously on a slightly smaller scale, a leotard (or one-piece swimsuit, there's no a whole lot of difference) morphing into a rather more revealing two-piece swimsuit.