If you have one or more Charms of Good Fortune, then whenever you kill a raid boss (in Raid Finder, normal or heroic) then a new UI window will pop up asking if you want to spend your Charm on a bonus roll. If you click yes, then you’ll instantly get another shot at that boss’s loot table! You will always win something from the bonus roll, such as a pile of gold, gems, or flasks. However, you also have a small (but not miniscule) chance of receiving a piece of epic loot. As with the personal loot system, the item will always be something designed for your current spec.
Is how Elder Charm of Good Fortune were described to work in the dev blog a while back. I am a bit confused on how current spec is determined. Is it when you pull/kill the boss or when you click for the bonus roll? Lets say I'm a tank but go dps for a one tank fight but still want the extra roll to give me a chance at tank loot. If current spec is determined on clicking for the bonus roll could I switch specs from dps back to tank before clicking to get a chance at tank loot from my bonus roll?