I intended to go paragraph-by-paragraph through your post and then completely forgot.
Subverting expectations and turning the game from political intrigues into a dungeon-crawl would not violate No Myth play. Drugging PCs is trickier, and, uhm... Depends.
In Dungeon World, if someone tries to Parley and rolls 6-, GM can make a move as hard as she likes, and it can be "reveal unwelcome truth": turns out, it was a trap! But then PCs are drugged because someone rolled 6-, not because the GM's notes say so. Whether catacombs were prepared in advance or invented on the spot is irrelevant.
Just saying "turns out it was a trap!" unprompted would be a violation of the rules of DW first and foremost, and feeling like this violation is justified by GM's notes that no one else at the table has seen would be a violation of No Myth.
Drastic change of tone is not, in itself, in a conflict with No Myth. It can be a breach of some other agreements ("hey, let's play a game of political intrigue!"), though, but that's another thing entirely.