2) Meat which requires salting, and the salt used in the kashering process
yes, that’s it!
3)one thing that was formerly kosher, after interacting with a second thing, is now pasul, the second thing that was assur, now after interacting with the first thing, becomes mutar. there is one interaction, one maaseh which accomplishes an opposite-like effect in two different objects (or persons). your scenario does not fulfill this.