Implement the new VI you would like to add to your palette. In this example we will make an event structure embedded inside a while loop that stop when a user close the window.
Give it a meaningful icon and name
Save it to
64bit: C:\Program Files\National Instruments\LabVIEW XXXX\user.lib, where XXXX is the LabVIEW version you have installed
32bit: C:\Program Files (x86)\National Instruments\LabVIEW XXXX\instr.lib, where XXXX is the LabVIEW version you have installed
Go to Tools » Advanced » Edit Palette Set
Navigate to the palette where you want to add your new instrument driver palette.