Doesn't really make sense since if it can talk to it, it will mine on it.
If it can't mine on it, then that would be coz it can't talk to it thus it can't tell it to turn the led off.
It is possible to enable/disable a device using the USB menu. I have sometimes slow nanofurys because of several reasons. To find them I disable and wait. Then I try to find the cold one. If the LED would be switched off, it would be much easier.
Disable doesn't currently turn them off, it just stops sending them work because the init sequence is involved and once they're running I try and not visit the init/shutdown code as the driver design assumes it will only ever be done once and prefers to just drop the device if it fails and lets it be hotplugged again if need be. I can revisit it.