The world headquarters will forward any letter from a witness or otherwise to the local congregation elders. Over the years I saw DF'd people write the society for help when a local BOE was uncooperative in reinstating the individual. Also, letters from people sending in for literature will be forwarded to the local BOE. So, any letter of inquiry about doctrinal questions will be in the hands of the BOE within days of its receipt in Brooklyn. So, if anyone wants the Wrath of GB down on their heads, just write the society about anything they've changed or is the least bit controversial. Better to save your postage and do your own research.
Elders routinely write the GB over questions the BOE has regarding the 'proper' handling of a multitude of situations, often at the direction of the PO. Usually, the answer is full of WT references, or the Elder's Manual guidelines.
Frankly, if you want to stay 'under the radar', the worst thing you can do is write the society with an honest question.