Disabling a specified usb port is not possible cause of USB is a bus system.
Rescanning devices are quite simple, there're many ways to achieve it, disconnect all or speciefied usb device by checking VID and PID of Device.
This link explains much better than I'm able to write now:
I would start trying this way (not yet tested) first:
1. Block all devices/access to usb at startup.
2. Detect if usb device has plugged in.
3. Check for right password.
4. If it's correct, enable device.
5. Check if device gets disconnected and block again.
Maybe you have to rescan it between some of this points.
Another good links (libraries):
A USB HID Component for C#
Hope that helps.
With Best Regards