I used to violate these rules some time ago. I set the PTR records for a corporate SNAT to the name "127.0.0.1." and it had the funny side effect I was expecting. Many forums listed me as coming from "127.0.0.x" making many moderators think I did something to their forums. People on IRC figured this out instantly. This was long ago. No idea what effect it would have today, if any. Anyway, the reason I mention this is that the DNS rules are rarely ever implemented as documented or intended or at least not consistently.