You can't just 'remove a limit' and let the player choose any. The race might exist (if it is complete), but all manner of coding isn't in the game. For example, the game hasn't been coded to allow the player to choose this new race from the menu. So, changing a value from 8 to 9 won't suddenly make a new team available in the menu and selectable.
You see where i'm coming from with this. If the team was available in the game as say, an unlock, then things would be very different.
You really can do that. It'd be a really crappy programming job if someone hardcoded those options in rather than read them out of the database - and if you need proof that it does that, go in and change the name of one of the races and see if it isn't updated in the pick-list when you start a new campaign.
Since the database has 9 records for race and only 8 are currently selectable, and because there is no flag in the database that determines if the race is human playable, there must exist a simple hardcoded cap in the display/selection routine.
If you manually change your race to 9, things play fine, so the entire race cap exists at the race selection screen.
Sure, and there are already references to race 10 and 11 being Undead and Norse. The modding community would love to add the missing 10+ races themselves, but the EXE has weak but hardcoded prevention of using any race above 8 (or now 9).