Probability Alteration is a set of abilities referenced:
3e[]
GURPS Spirits pg 34 a basic power of spirits following Poltergeist Effect though some are not able to do it as a -20% limitation to the 100pt Spirit From template, saving 20 points.
4e[]
pg 43 of Psionic Powers uses it for a category of psionic powers including:
- Adjustment made from Visualization
- Coincidence made from Serepipity
- Curse made from Affliction
- Second Chance made from Luck
- Weather Control made from Control Weather