A search of the web shows that you can stain over shellac, but you pretty much have to then apply more shellac over the top of it to seal the colour in. As McCreed says, the stain won't penetrate it, so will sit on top, and without protection, it will rub off. My gut feeling is that without spraying on the shellac over the stain, at least the first few coats, you're likely to rub off stain in patches if you rub on more shellac.

There are a whole list of things that are possible to do, but very few of them are the best way to do things.