Here are ways to bring back a snuff that has dried out in storage. Drops of water work straight away and the other three take a night. A dried snuff tastes stronger, probably because the alkalisers make up more of what's left, so putting the water back should bring back its usual strength.
Overnight for the first three methods. Drops of water work straight away.
Notes
The slower methods are harder to overdo, but the longer you leave them the damper the snuff gets, so check it the next morning. Take the carrot out once the snuff is moist, because fresh food left in a tin can go mouldy. For something longer-lasting, cut florist's foam to fit a small tin, wet it and punch a few small holes in the lid, and you have a tiny humidifier to leave inside a bigger tin. To put back exactly the water a snuff has lost, see Rehydrating dried snuff by weight.