>what steps should a candidate take to avoid completing such tests and investing personal time that results only in giving the company free performance data?

Probably nothing different. I suspect that investing additional time and energy is not going to be a net win for you.

>The revised ad also made it sound like the position was far more junior than when I initially interviewed.

It is possible that there was discussion internally and they decided against paying whatever it would cost to hire someone like you. "We're not paying that, get a new grad" is not an uncommon refrain in some circles. If it helps, places that like are usually not nice places to work.