I cannot say how this plays out under US administrative law, so take this as comparison only. Here, only a Delegated or Implementing Regulation under the Union Customs Code can withdraw a relief such as inward processing; a national authority's own guidance note has no power to narrow it, however firmly worded. Where one has tried, traders have taken it to the customs tribunal and had the guidance set aside, the regulation left standing.
Under EU dual-use export control rules the same split holds: only a Commission delegated act changes the control list. Guidance from a licensing authority, however detailed, cannot narrow or widen it on its own. I have seen a shipment held up on an FAQ's word, and the annex never moved. I do not know how CBP bulletins rank against the order under US law, but the shape looks familiar.
