Hawk, this is theoretically possible. There are companies which never change the basic parameters in the FMC, others do this on a monthly basis with the latest analyses from the fleet.
There are plenty of factors which all feed in to the system and calculate the individual parameters, using an optimization tool will provide a cost index which is not (!) reflecting the present optimum, but the one based on the last calculation data.
Worked for a company which was very particular about the CI, however, as per directive of the DO, during climb and descend we used a fixed speed setting.....makes the whole game a farce.
Presently using 34 for all classic flights and in during all stages.