Correct, this is currently the only way to currently clear any applied white/black list.
But if you have sent the white list with the retain option, your MQTT broker will send it again to reapply it after a restart of your OMG. Just make sure you send your white list with the RETAIN option.
Since I require different white lists in my setup, depending on various other conditions, I programmatically restart OMG, then catch the LWT topic and reapply a different white list depending on the circumstances.
So two possibilities to make sure your white list is always being applied.
If you searched through the forum, you might have seen how I came to the above solution, when I asked about the possibility of reducing or clearing a white list 