Hi,
while the Mach website is be re-designed the search function is on the blink.
Not sure about the shuttle pro but there are a number of API's specifically to deal with jogging. This one sets the jog inrement:
LUA Syntax: 
rc = mc.mcJogSetInc(
      number mInst, 
      number axisId, 
      number increment)
Is it possible to have a shuttle pro button trigger a macro? If so then judicious use of this API could do the job.
Craig