There would be a huge benefit to creating two separate wearable objects one with the shape settings for heads and another with the settings for bodies. If dividing the base shape is not feasible then having a built in official way to manage the settings for each and upload/download them as needed would be a good alternative. Actual shapes though make it very easy when swapping a head to simply wear the appropriate shape.
Another alternative would be to allow shape settings to be adjusted via LSL.