Subrule · Chapter 9
cr:9.2.2b
If an effect instructs a player to name a card,[8.5.21] they may name one of the two split-card names, but not both.
Example: Chains of Eminence has the text “When this enters the arena, name a card. The named card can’t be pitched, played, or defend while this is in the arena.” If the named card is “Shock”, the split-card Regrowth||Shock cannot be pitched, played as Shock or Regrowth||Shock, or defend; but it can be played as Regrowth.