Changing the rod length won't change the compression ratio either. Only if the deck height doesn't change. You could even have a lower compression ratio if while lengthening the rod you raised the deck height. Shave some off the top of the liner and you raise the Comp Ratio. To many variables to make that statement. The only exact thing is the stroke is based soley on the distance of the crankpin and crankshaft centers and it is a constant given a given crankshaft.

It's called geometry and I taught it in high school.