Alcohol will damage all shellac finishes as it is the solvent used in shellac.
Alcohol is a solvent.
Follow directions for handling. Shellac made from raw flakes has a shelf-life of approximately 6 months before it becomes a gummy mess. The manufacturers of pre-mixed shellac claim a shelf life of 3 years. When using shellac flakes, dissolve the required amount of flakes in alcohol by mashing the flakes up and stirring them into solution. For pre-mixed shellac, adjust the concentration by checking the package and adding more solvent to the solution.