We would like to precalculate approx 100 frequencies. Can I calculate all my frequencies from doing only one reset or recall on the NVM then load them as need using the DCO freeze, load registers, unfreeze DCO, New Freq without doing a reset or recall NVM each time?
Yes you can write the registers for each new frequency without first recalling the NVM. The DCO freeze operation allows direct writing of the frequency registers to the required values. DCO unfreeze + New Freq initiates the internal state machine to start using those register values in operation. An NVM recall operation is only needed if you want to return a device to factory settings.
Note that each Si570 device will have a slightly different internal crystal frequency so it is necessary to pre-calculate register values for each device separately for maximum frequency accuracy. You cannot use the internal crystal frequency of one device as the basis for calculating the register settings for other devices without having frequency offset errors. This is described in the Si570 datasheet.