Yes, JTAG pin numbers 2 and 10 (which are ground pins) are connected together in the USB-Blaster™ programming cable. You can use this feature to design a circuitry selector by pulling-up either pins 2 or 10 on the board. When the USB-Blaster cable is not plugged-in, the pullup line is active, when the USB-Blaster cable is plugged-in, the pullup line will be overriden by the internal ground connection inside the USB-Blaster cable.
For more information on the USB-Blaster, refer to the USB-Blaster Download Cable Userguide (PDF).