When playing a Reaction in Riftbound, what decisions must be finalized before the next Reaction can be played, and can those decisions be changed later?

Ruling: When a Reaction is added to the Chain, only targets and move destinations must be finalized before the next Reaction can be played. These decisions cannot be changed later.

Nuances:

• Certain decisions are NOT finalized when playing the Reaction, but rather when it resolves: which card to discard, how much to pay for cards with payment choices, whether to execute optional effects, choices made by multiple players, and some other rare exceptions
• The only exception to decisions being unchangeable is Mystic Reversal