Can I change my Chosen Champion during sideboarding?

Yes, you can change your Chosen Champion during the sideboarding process.

According to Tournament Rules Rule 403.4.a: "During that time [sideboarding], a player may change their Chosen Champion to one from their sideboard or Main Deck that meets the deckbuilding rules of the competition format."

When doing so, keep these points in mind:

• 1-for-1 Exchange: Sideboard cards must be exchanged 1-for-1 with Main Deck cards (Rule 403.4).
• Deckbuilding Rules: Your new Chosen Champion must still align with your Champion Legend's tag requirements and your deck's Domain Identity.
• Fixed Elements: While you can change your Chosen Champion, you are not permitted to change your Champion Legend, Rune Deck, or Battlefields after deck registration in constructed formats (Rule 403.4.b).