turn off 600ex confirm light blink

Is there a way to turn off the 600ex rt confirm wireless link red light blinking?

In some instances it's a bit annoying.

found it..

Since the first EX-series Speedlites of 1998 with wireless flash capability, Canon Speedlites used as off-camera slave units have given photographers a visible indication that they’ve recycled by flashing the red AF-assist beam on the front of the unit once per second. Speedlite 600EX-RT also does this by default but for the first time, a Speedlite Custom Function now allows users to disable this (the only “ready” light on the slave unit would be the rear pilot lamp). Option “1” achieves this, if it’s needed to prevent the illumination from appearing in long-exposure images or to conserve a bit of battery power.