Let me see if I understand this correctly...
On any given bike, changing the length of the cranks should mean changing the saddle height and fore/aft position: longer cranks = saddle lower & further back; shorter cranks = saddle higher and forward. Granted, most of the readily available/common crank lengths vary by about 5%, so the saddle adjustments will be small.
What I find curious is that we have responses indicating inseam length variations of 20%+, yet crank lengths vary by +/-5%.