Ive seen people label their ketchup or mustard or other condiments in their home as either meaty or milky or parve. How does a condiment's kosher status get changed?
It's just a good practice as often kids may touch the ketchup bottle to the hamburger/pizza/mac&cheese when spreading ketchup on it, or their hands are messy. Stuff like that. (Especially if they have two refrigerators, you keep a bottle in each!)
Shulchan Aruch talks about separate salt cellars, but that's because people would dip their bread, cheese, or meat into the cellar, leaving behind little bits of meat. The commentaries there discuss, and reject, the idea that a salt shaker would really be milchig or fleishig.