Crusader Kings II - Mod General

[rickinator9]

#Child is born of Aurthorian Blood
character_event = {
 id = 3000000
 desc = EVTDESC3000000
 picture = GFX_evt_birth

 max_age = 1
 trigger = {
  OR = {
  father_even_if_dead = { trait = bloodline00 }
  mother = { trait = bloodline00 }
 }
  NOT = { trait = bloodline00 }
 }

 mean_time_to_happen = { days = 1 }

 option = {
  name = EVTOPTA3000000
  trait = bloodline00
 }
}

Should be:

namespace = blood

#Child is born of Aurthorian Blood
character_event = {
 id = blood.1
 desc = "blood.1.desc"
 picture = GFX_evt_birth

 max_age = 1
 trigger = {
  OR = {
  father_even_if_dead = { trait = bloodline00 }
  mother = { trait = bloodline00 }
 }
  NOT = { trait = bloodline00 }
 }

 mean_time_to_happen = { days = 1 }

 option = {
  name = "blood.11.option"
  add_trait = bloodline00
 }
}

I would always advise you to use namespaces. They work great for compatibility with other mods and official PI patches.
'trait =' is a condition which checks if someone has the designated trait. 'add_trait' is a command which adds the designated trait to the character.