Speculation:
Since the lac sticks appear to be colored shellac, and ethanol alcohol is the preferred solvent, perhaps the lifetime limit is due to the stick becoming hard as the alcohol slowly evaporates. The video shows a metal bowl with a clear liquid the person adds to the mixture; perhaps that’s the alcohol. Perhaps the life of the sticks could be extended by storing them in a tight glass container with a bit of alcohol in the bottom.
Since rubbing the lac sticks on the wood appears to be a method of applying friction polish. This was documented in an article by an English explorer in India in the 1600’s who watched a craftsman turn “household items” then apply lac bug secretions to the spinning wood with friction. I suspect color in some form (dye? pigment?) could be added to today’s off-the-shelf friction polish such as the shellac-based Mylands. However, that stuff goes on pretty thin and requires multiple coats to get the “high build” advertised on the can’s label.
I’ve applied Mylands friction polish over color on the wood but I don’t remember what I eventually did to prevent color bleeding from the heat and the alcohol - I might have used pigment-based colored india ink, wonderful stuff.
JKJ