For gutter mount Yak racks it depends on whether you expect to need to lock them again. The lock operates by pushing out a plunger that engages with the outer portion of the rack foot, which is plastic. The plunger is just a screw that inserts into the lock cylinder. If you turn the knob hard enough, it will either tear its way out or break/bend the screw, and at 90 degrees from locked, the screw will be revealed. Just unscrew it, and the knob will turn, and the cylinder will just fall out. Of course you've now messed up the lockability of the foot. There are two locking slots, 180 degrees apart, so you could still use the locks if you turn the knob to the undamaged side.
As an alternative to tearing, if you can figure out which side the plunger is currently at, you can drill a hole through the plastic of the foot, and unscrew the plunger from the cylinder. This will not damage the locking ability of the foot, though of course a thief who noticed the hole could unscrew the cylinder again. However, considering how marginal the locking system is to start with, it might not be much of a loss. You could, perhaps, plug the hole later. A thief who is determined to steal your racks can do so with a medium sized pipe wrench or a pry bar more quickly than he could with a screwdriver through the holes anyway.
