[Q]

Racial immunity against specific weapons:
Racial traits (modable of course) that make a race completely immune to one or several weapon types. E.g. energy life forms like the Eee would be immune to projectile weapons or certain organic weapons (can acid globules harm energy life forms?). Or mechanic life forms would be immune to allegiance subverter.
In the trait you specify the weapon families that have no effect and then you simply could not target the race with theese weapons.