When a new MIDi device is connected to the PC, VST Live has to be close and reopen to detect new device.
It should detect new devices without restarting the soft.
VST Live deliberately does not check for device changes, as that may be fatal during a gig. Some changes you make outside (i.e. buffer size/latency, sample rate etc) may cause actions triggered by drivers though.
However we are planning a preference or temporal state so check for device changes.