Has anyone ever applied shellac over lacquer when refinishing furniture? I know this is not an ideal refinishing strategy.

I've done it once or twice but as you said it's not the best. Mainly because if you use lacquer over lacquer the new coat will partially melt the old one and bite into it better. It will also melt and flow out any scratches or marks to some extent.

Generally though you can put shellac over almost anything.

Shellac over lacquer is perfectly fine. I do this all the time. I need to build a finish fast and then just continue with shellac. I even lacquer the last coat sometimes over shellac.

Fred