[jpatokal]

Well, that's the thing: since it's not an embassy, it doesn't have an ambassador with diplomatic privileges, it has a "chief".

But my point is that this is all just paper. Out in the real world, the US can (and probably will) pretty much just swap out the plaque outside the "US Interests Section" with one that says "US Embassy", with the chief and their assistants magically transformed into diplomats.