V8 supports one debug port per isolate/runtime, although, to be honest, we've never tested multiple debug ports in a single process.
Once you've enabled debugging in a given isolate/runtime, you can't reconfigure or disable it via any API. Debug flags and ports specified subsequently for the same isolate/runtime are ignored.
By the way, be aware that V8 5.6 dropped support for the original V8 debug protocol, so debug behavior is likely to change in future ClearScript versions.
Once you've enabled debugging in a given isolate/runtime, you can't reconfigure or disable it via any API. Debug flags and ports specified subsequently for the same isolate/runtime are ignored.
By the way, be aware that V8 5.6 dropped support for the original V8 debug protocol, so debug behavior is likely to change in future ClearScript versions.