No ... because what if the unlock actually damages the card to the point that it no longer works PERIOD ... with the 6970 bios on it? You'll never be able to remove it before you RMA because the card is dead. In fact, even if it completely died for any reason ... say, in 6 months time ...
you could run into this problem.
Actually, a 6-pin plug can pull just as much power as an 8-pin plug ... as long as, you know ... the wires don't catch fire from the excessive power draw. And that's pretty unlikely, frankly. I doubt that just having 2x6pin connectors rather than a 6pin + 8pin is going to impact max OC-ability.