Certain multigrade filters claim an invariant exposure time between grades, or they provide a factor to calculate the new exposure time at the new contrast grades. Assume this works as it is supposed to.

So I make a test print. If my blacks are both too grey, and my whites are too grey, I suppose you can switch to the next-highest contrast grade and use the same exposure.

Now, suppose I make a print that needs more contrast. I find that the blacks are black enough, but the whites are grey. I switch to the next higher contrast grade. Should I change my exposure?

Suppose my current print has fine whites, but the blacks are too grey. I could increase my exposure to make the blacks blacker, but suppose I judge that that would wash out my highlights. I changed to the next highest contrast grade. Should I change my exposure in this case?