Hi, have read with interest the many ways you could use a french polish over different stains, I have used nearly every type of paint and stain under shellac,
I had a hobby e few years back Graining the metal work on Vintage cars,This was on metal mostly, the parts would come to me repaired and primed in auto primer.I would depending on what type of wood finish they wantedI would some times use auto colour or oil colour for the back ground work, then grain in oil stain,when thorouly dry would over grain in water,using a talc dusting to over come the oil ,then two thin coats of shellac when again dry,have used water ,oil, and lacquer finish,What I am saying is that if you spray the shellac on you will not disturb the stains, But using a brush or rubber to apply the shellac you will lift the previous coat, spray the shellac on you can just about seal off most of the different stain's.when you french pollish
You should not bedisturbing the shellac because you will be buildind the coats up.
For instance painters knotting which is laquer based is used to hold back weeping knots in the timber,also will seal water stains on ceiling and walls.I have put apic in to show how the different paints are protected by the lacquer just my thoughts .