I understand CVT. For a regular transmission, all the gears and ratios are set. If Nissan want to change the performance or MPG, they can change the gear ratios. Actual metal parts.

On a CVT, could Nissan do it? Would it be something electronic or mechanical?

Maybe the question would be, would the CVT ratios be the same between years 07, 08, 09, etc, etc?

Two things they could do, at least. One, the easiest, is to change the final drive. The CVT output pulley drives ring/pinion that turns the axles, through the differential. Changing those gears would be easiest. With the 3.5, the final drive ratio is 5.173:1. It could easily be changed for less rpms/more economy.The other thing they could do is to change the diameters of the drive/driven pulleys inside the CVT. MUCH harder, MUCH more $$$, might require a new case, new belt.