Yes, I'm using simple examples to demonstrate a particular difference, because using "real" examples makes getting the point across a lot harder.
You're also just wrong. I did in fact test, and both GPT 3.5 Turbo and 4o failed. Not only with the rule change, but with the mere task of providing possible moves. I only included the admission that they may succeed as a matter of due diligence, in that I cannot conclusively rule out they can't get the right answer because of the randomization and API-specific pre-prompting involved.
> "For chess board r1bk3r/p2pBpNp/n4n2/1p1NP2P/6P1/3P4/P1P1K3/q5b1 (FEN notation), what are the available moves for pawn B5"