Frank, I think you should read back several months' worth of the SE forum on this site if you haven't already done so. There is a LOT of info embedded in there, either explicitly or implictly, on how and what to block.
Yahoo is VERY much a minor irritation compared with some of the very real attacks, scrapes, spams and general scum hits that are around. As caribguy said, concentrating on killing yahoo is missing the point: concentrate on killing scum and yahoo will drop into the trap IF they misbehave, even if their intentions are "honourable". That is precisely what happens on my multi-site server.
The worst attack I sustained on my server so far this year has been from a bank/creditcard sponsored "security" service. They dragged down my server almost completely for about 45 minutes one night without my permission: the "page urls" they tried were on the lines of the yahoo ones but far more extensive (and yet ultimately stupid and useless as security checks). The server stood up to it because the ("home-made") infrastructure was designed to block such attacks.
Fix the underpinnings and let yahoo wander at will - until it hits the traps and blocks itself.