I think that you may mean Silver Nitrate as sodium nitrate is generally regarded as a fertilizer and foliar feeding with it would not sex reverse the plants.The true way to do this is to stress one female, collect that pollen, and then use it on an identical, healthy female. Then you have feminized seeds. The way you're suggesting will pass on those stress traits to your seeds, and you'll most likely have ALL herms with those beans.
The way you stress a healthy female is with sodium nitrate via foliar feeding.