[T-Ricks]

After you pay the cost for B'Elanna Torres Creative Engineer to use her ability, can your opponent change their mind and not discard a card, assuming they have a choice?

[GooeyChewie]

No, the opponent has committed to discarding a card by the time you use Torres. In a friendly game, if it’s obvious that my opponent forgot I had Torres (rather than is fishing to see if I’ll use her), I’d likely let them take back the action - but if so I’m also not paying for Torres’ ability.