MSP430 Bluetooth interfering with USB module
The Arduino has the same issue, and they have implemented a fix a long time ago.



As you can see in the image, Resistors RN4B and RN4A are 1k series resistors between the USB-Serial ic and the Arduino's ATMega328p. This allows a device connected directly to the Arduino headers, like a shield/boosterpack to communicate with the Arduino without interference from the USB-Serial IC.

You want to implement the same thing. Place 1k resistors between your MSP430 and your Bluetooth module. This will mean that the USB-Serial connection has precedence over the Bluetooth module. Any communication between the USB-Serial and the MSP430 will not be interfered by the Bluetooth module. That said, you cannot send/receive from the bluetooth module when the USB-Serial connection is plugged in.

Update: This may not always work though. Some devices, when there is no usb signal on one side, will turn the tx/rx into floating/open inputs, instead of driving the line, which is good, but others, when off can still siphon power via clamping diodes in gpio pins. It can be a pain because this means they attempt to drive the line, preventing others from doing so.. In your case, you might need a bi-directional multiplexer, or simpler, if the usb serial is only occasionally used, you could add a jumper to the line. Plug in the jumper when you need to use the usb connection, remove it when you don't.