How to connect chip pin to either vcc or groud externally?
Here's a picture of the typical setup to do this:


In your case you would use only 3 posts, the center being the pin you want to switch, and the ends being VCC and ground (VSS). These "breakaway" headers and shorting plugs are readily available from Digi-Key or Fry's, etc.

As one of the comments pointed out your diagram is labelled VSS and ground, which sounds incorrect.

The other comment suggests zero ohm resistors which is also a great solution if you don't need the flexibility of changing back and forth a lot. A "stuffing option" at the time of manufacture can select the correct setting.

Finally you could use solid state switches or a relay if you wanted to make the selection via a microcontroller or some other automatic method.