Unfortunately, it is not possible at this moment. This requires Core Tunnel removes "-T" and "-N" options, I have to do some test deliberately before removing "-TN". Will update this thread once we find a solution.
Core Tunnel version 1.7 now can execute you command by setting RemoteCommand to:
bash --init-file <(kill -9 $(lsof -ti tcp:9000))
You may notice I removed sudo from the command on purpose, since Core Tunnel do not have a terminal window like Core Shell, so it could not react to password input which sudo would require.
bash --init-file < prefix makes sure the tunnel can persists after command is executed, otherwise, the connection will be disconnected immediately afterward.