Starters are dependent on the number of pit stalls available on the track. Have more starters than the track normally allows, and things will get a bit funky.
However, if you are going to run races that require no pitting, then its theoretically possible.
The reason why I say "theoretically" is because I attempted to change the max starters at Richmond from 39 to 43, and the game kept crashing. I don't know how it affects other computers.