nvaddtrapconf can be used to load trapd.conf automatically in lieu of doing it 
manually with Options->Event Configuration->Trap Customization: SNMP....

But I have not been able to persuade nvaddtrapconf to add new event categories. 
 

If I create a file 't' containing:
  CATEGORY 10 "New Category"
and attempt to merge it with the command:
  nvaddtrapdconf t 
the response is:
  ERROR: Bad new CATEGORY
  NOT ADDED: CATEGORY 10 "New Category"

Varying the category number seems to make no difference.

Has anyone been able to add new event categories through nvaddtrapconf?
Thank you,
William Schumann