So you treat the MDA as a DA which it was not intended to be treated as? Nor is it legal do descend below, for that matter, unlike an actual DA, which is designed with the assumption that it is the altitude where the *decision* to continue or miss will be made, and the inevitable descent below is assumed?
You can set a DA (using the NPA MDA) for a non precision approach. Yes, you will descend slightly below DA in the event of a missed approach. The approval is contained in many airlines Ops Specs these days. There are limitations on the procedure that provide obstacle clearence etc.