[Suicide Junkie]

Note that there is nothing stopping you from verbally declaring certain racial techs to be mutually exclusive.

P&N has the mutually exclusive Pirates, Nomads, and Nomal traits, for example.

Adamant mod has lots...


If players must choose one from a set of traits, and a race is not viable if none are chosen, then you can do the following:
1) Create a dummy trait that does nothing, and costs -50000
2) Set the cost for all your exclusive traits to +50000

Thus, the players have to choose one and only one.