Can varnish be applied over french polish?

Usually no. Shellac has wax in it, and you use linseed oil when applying a French polish. If you painted that, the paint would peel off. If you want to paint a French-polished piece, you need to remove the polish first. Alcohol would be your best bet.

if you add the polish over the french polish it will ruin the french polish. i have tried it before. << Actually, I think the questioner's trying to turn the item from a French-polished piece to a painted one. If he does that without stripping the item, it'll ruin both the French polish (which is notoriously delicate) and the paint. But yes, you're absolutely right it will ruin the French polish--looking at French polish crosswise ruins French polish, so what else is new?