A couple of years ago I asked about varnishing over shellac on some bathroom doors. The old thread is at
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any rate, one fine day when the family was gone and I could open the windows and doors, I got lazy and just gave the doors and cabinets a quick scuff with some 320 sandpaper and slapped a fresh coat of shellac over the damaged areas; a couple of coats over the worst areas.
The results have been spectacular! You can't tell where the finish had previously been dulled and rough. Now it's nice and shiny. It was so easy (I love shellac) that I think I'll just do it every year or so as a quick preventative.
Thanks again to the NG.