Hope it works for ya. I tried once to go over existing shellac and ended up with a mess. Hope you have better luck with it than I did. If all else fails can always easily strip old shellac with lacquer thinner or other solvent, clean wood with Oxyclean and reapply shellac finish. For brushes I've used the 1" wide foam brushes. A large pack is a few bucks and just throw away after one use.
Are the markings you want to preserve in the shellac itself or under in the wood? If they are in the wood, they are easily preserved.
Have fun with the shellac. It's really very easy and you can experiment with colors and variations. Your imagination is the only limit. Here's a Romy I redid (I took a little liberty with adding the Polish PG instead of the Romy PG - just liked the color match better). I saw an AK BigAl did and wanted to do one very similiar. He got me started with shellacing AKs