Will you always have a 2016 column for [Category]? If so, I'm not sure Tableau is going to want to display the ∆ column conditionally.
But I would start with loading nulls into the ∆ calc when your "hide" condition is met. See what that does for you.
And if ∆ is not a calc, then make a calc that says something like this:
if (condition met) then NULL else sum([∆]) END
and display that instead of ∆ itself.
Depending on what Tableau does with that, if the column doesn't go away entirely if all NULLs are in it, then we can pop out an opaque container on the dashboard that masks the column when "condition is met".