What to do when you've Marked "overwritten" stats?

Setup: Pox is a Gunlugger who took the "Battle-Hardened" gunlugger move, rolling Hard insterad of Cool when under fire. Pox will now never roll Cool unless either A) the MC decides to use the optional battle moves and Pox opts to provide covering fire (the only other stock Cool move in the book that I can find) or B) the MC has developed some custom Threat moves which force him to roll Cool.

Problem: Another player at the table marked Pox's Cool for advancement.

Question: How does this get resolved most easily?

If he did it after Pox took "Battle-Hardened", it's pointless so I would convice this "another player" to choose another stat.
If it was before, it would be nice for Pox to change highlight at the first ocassion.

"Hey, I'm never going to roll cool. Highlight something else, yeah?"

-Vincent

Awesome. S'what we've been doing, and everyone's been cool with it. I was half-expecting a burning wheel forums-esque "That's life, he must deal with it" response, but figured I'd ask anyway. Rock on. Thanks =)