Update a Multiselect List with .add?

Update a Multiselect List with .add?

  1. bool helpers.testing(Events event)
  2. {
  3. info event.Event_Specifics_List;
  4.   event.Event_Specifics_List.add(3206171000012706003);
  5. info event.Event_Specifics_List;
  6. return false;
  7. }

Hey folks, inside the form Events I've got a Multiselect Lookup setup. I need to update some of our Events en masse to include an additional value to this lookup, so trying to setup a quick function to do that.

I'm confused why this doesn't seem to work. Here's what those two Info's return:

3206171000006149003,3206171000008994003,3206171000008994008,3206171000008994024,3206171000008994029,3206171000008994046,3206171000010117024,3206171000011381004,3206171000012362007,3206171000012362016,3206171000012563007

3206171000006149003,3206171000008994003,3206171000008994008,3206171000008994024,3206171000008994029,3206171000008994046,3206171000010117024,3206171000011381004,3206171000012362007,3206171000012362016,3206171000012563007

Thanks for any help!