I am doing a melomel and am putting some mangos in primary and again into secondary a month later.
I was going to put pectic enzyme into primary, do I need to put additional into the secondary?
Enzymes are catalysts and are not used up in the process of converting the substrate, that much is true. However, enzymes are not being introduced into a stable environment when being put into your melomel. Think about it, there is alcohol, the pH is very low, there is nothing to stabilize the enzymes, etc. Most likely the enzymes added in the beginning are dead(denatured) within the first week.
It would be a good idea to dose again when more mangoes are added for increased extraction, or add the enzymes later for clarification purposes.
As with all catalysts, enzymes are not consumed by the reactions they catalyze [...]
In other words, once you've added the enzyme, it will still be around to break down more fruit later (assuming you've not boiled the enzyme, which denatures it, but of course that's not the case here.)
So, you shouldn't need to add more to secondary since the enzyme will be carried over from primary.