Hi,
no.....you don't need to program how Mach is to jog.....it knows how to do that already.

The attached pic is the event properties of the X axis jog button. Thus if you have a button <X Jog> then it would simply call the stock actions.

In your case you wish to use an axis selector switch and an MPG. You will need to attach, albeit temporarily, an axis to your MPG:

LUA Syntax:
rc = mc.mcMpgSetAxis(
      number mInst,
      number mpg,
      number axis)

Where the axis ID is provided by reading the axis selector inputs.

The movement is given by:

LUA Syntax:
rc = mc.mcMpgMoveCounts(
      number mInst,
      number mpg,
      number deltaCounts)

Craig