script for port 443 and 50000-59999

I think you want to check TCP::local_port not TCP::client_port. TCP::client_port is the source port.

You can check for the ports you want to allow using this:

([TCP::local_port] >= 50000 && [TCP::local_port] <= 59999) || [TCP::local_port] == 443)

And you can logically NOT that to drop everything else:

 
 when CLIENT_ACCEPTED { 
  
     Check requested port 
    if { ! (([TCP::local_port] >= 50000 && [TCP::local_port] <= 59999) || [TCP::local_port] == 443)}{ 
  
        Request was to an disallowed port, so drop it 
       drop 
    } 
 } 
 

Aaron