Does a rule exist requiring players to stick to target choices announced for reflexive triggers before a spell like Falling Star resolves, as long as those targets remain legal?

Ruling: Yes, this rule exists in the tournament rules. When a player puts a spell or ability on the chain and announces choices (including targets) that are normally made upon resolution, they must adhere to those choices unless their opponents react.

Sequence:

• Player plays Falling Star and may announce intended targets for the reflexive triggers as a shortcut
• If opponent does not react, the spell resolves and the player must use the announced targets for the reflexive triggers
• If opponent reacts at any point, the player may need to choose different targets when the reflexive triggers are actually placed on the chain

Nuances:

• This is considered a common shortcut for tournament play to allow concise communication
• If a player announces "Falling Star targeting these units" and the opponent responds ambiguously, the responding player should clarify whether they're responding to the spell itself or to the reflexive triggers
• If responding to the spell before it resolves (like with Retreat), the original announced targets may no longer be valid, forcing new target selection
• Players should not use this rule to misrepresent game state or angle shoot by claiming their spell hasn't resolved after an opponent responds
• The rule applies to choices beyond just targets (like with Bullet Time)