I did receive a nice reply from SCCA.
This happened to be a SuperTour event - considered the 'National Series'.
Travel plans is 1 of 3 reasons they cannot change groupings. Numbers and 'changing the product' are the other 2.
It seems SuperTour IS less flexible.
My bad. My advice: Monitor the upcoming event and cancel if the groupings look bad. I'm not sure how many people attend more than 1 SuperTour event. Got to be a small number.