Players participating in Limited tournaments that do not use decklists may freely change the composition of their decks between matches by exchanging cards from their deck for cards in their sideboard without being required to return their deck to its original composition before their next match. The Head Judge or Tournament Organizer must inform players if this option is not being used prior to the start of deckbuilding. This option is not available at Competitive or Professional Rules Enforcement Level tournaments.
The default for events that do not have a decklist is continuous construction. Remember that Competitive and Professional Rules Enforcement Level events should have decklists, and thus the original composition needs to be restored prior to the start of each match.