Can only redirect an ability that uses the word "choose" (e.g. not Tears of Lys or Ghaston Grey).
Targets are normally chosen before the ability's effects can be cancelled (except for post-Then effects, e.g. Ser Gregor and The Tickler).
To check eligibility, see if the new target could have been chosen as a valid target for the original ability.
- Can redirect His Viper Eyes and Yoren's ability to an eligible The Seven character in your hand / discard pile.