I don't recall that it is possible to disable the "all" channel....if you're referring to channel 1 - All Countries - channel
That is why HTC disabled it in AH/AH2 , except for sending salutes only....so if a player wanted to text/talk across country, they did it at their own choice, by tuning to ch200
Have you tried .squelch radio 1
or .squelch channel 1
Hope this helps
TC