Is there a way to change the starting population for the player race in a new game? I'm trying to do a conventional start with a mostly-accurate population for Earth (i.e. several billion rather than 500 million).
Turn on SpaceMaster (Crystal Ball, second from right end) and you can edit population (and installation) numbers on Colony window.
Of course, to more easily reset all your "stuff" to the 500 million level it's easier to delete the colony of Earth, then the Human race, then use System View (star with planets against black background button, in the middle) to select Earth and "Create Race" (bottom right) and walk through race creation all over again.
-- Please note this will produce slightly different Humans, but personally I consider that a
good thing.