If you remove the packing on a GYTR exhaust on an 07 Yamaha R6 will it give more horsepower and will it damage the motor from noless back pressure?

I wouldn't have thought exhaust end-can packing would significantly increase power output, or reduce back-pressure. That is normally dealt with by the tuned length of the pipe itself and overall diameter of the exhaust-can internals. Removing the packing will obviously make it noisier, reduce any heat build-up and possible reduce the weight, but only a little. Other than that I don't think there will be much in the way of performance enhancements to be gained. If you however remove the internal pipe work inside the exhaust-can and install a straight-through internal pipe, with custom packaging I would have thought this would give more impressive power gains. The first area for exhaust modifications on a modern bike should really be at the Catalyst end. This device reduces power output, increases weight and heat.