>how does one engage VR effectively in the recomposed position >without losing the focus lock established before the >recomposition took place?
The problem here (in most exposure modes) stems from crowding three functions (exposure, focus, VR) simultaneously into one button press. By setting AE-L/AF-L to Focus On (f4) you remove one of those functions. Once you have achieved focus and removed your thumb from the button, i.e., you have locked focus, the camera will fire whether or not your release priority (a1, a2) is Focus or Release. Then the shutter button is doing only double duty (AE-L and VR). If you shoot in M, the shutter button is only controlling VR. This describes my default settings.
That said, it's critical to recognize that we're talking about low light, slow shutter speeds and wide apertures here. With its stellar high-iso performance, the D600 can help keep shutter speeds up in reasonable territory. The wider the aperture (either discretionary to control background look or forced by the situation), the closer you get, the thinner the DOF and, consequently, the easier it is to lose your depth of field when recomposing. I'm fairly agile and athletic and can vouch for the difficulty of this move. I often find myself refocusing by subtly shifting my posture in the recomposed position. Recomposing a subject into a corner where sharp focus is to be found at a different focus setting (typically a greater problem with FX than DX) is an entirely different matter but still wholly operator error. I don't think I can remember an instance where it was clear that any particular loss of focus was the fault of the camera alone.