I'm expecting a fast FAQ on this one, but, here's the new character rule.http://i.4cdn.org/tg/1512114809065.jpg
There's one intended difference, and differences I believe are unintended.
First up, the intended change is simply clarification, as seen in recent FAQs and commentary:
Characters must be the closest target, no ifs, ands, or buts. If another unit is hiding behind a wall, but is closer, you still can't target the character. This was intended to prevent "Rhino sniping," where a player uses large, blocky vehicles to obscure other units, so that the, "nearest visible" target was a character.
The first unintended difference, is the change from "Wounds Characteristic" to simple "Wounds." A person could easily exploit this to argue that a when a large character model is reduced to 9 wounds, they become immune to targeting.
The second unintended change is the loss of the "shooting phase" restriction, which means characters are no untargetable during overwatch, even if they charge first, should another unit be closer when the character declares the charge. For T'au, this also affects our cooperative overwatches.
Again, I believe that these two "side effects," will be errata'd quickly, but it is up to you, the individual player, to determine whether these changes are valid in your games.