addInformation does add tooltips, but I think that Multimap func_111205_h() is the one I was thinking of.
If you're trying to override it and then get the multimap for your own purposes, super.func_111205_h() will give you what ItemSword is already adding, which you don't want. You'd have to look at the base Item class's implementation.
You are right.
Before, I tried overriding and setting custom value, but it didn't work because the first line is "Multimap multimap = super.func_111205_h();"
Super (in this case) is not Item, but ItemSword, so the returned multimap already had the value set.
I looked up the overridden Item method, ant it was simply returning "HashMultimap.create();".
Finally, I changed the method to create a new Multimap, and now it's showing the info correctly.
Thank you!