What are the rules for the Modified Champion Deck format used in launch events?

Ruling: You play with a champion deck and can swap any cards with ones pulled from the booster packs (from the champion deck or additional 2 packs if available), with normal deck-building restrictions applying. The deck has both a 40 card minimum and maximum, so cards from booster packs can only be added if other cards are removed.

Nuances:

• Sideboard rules are unclear from this discussion - assumed to be no sideboard in Bo1 and yes sideboard in Bo3, but unconfirmed
• Your whole pool may function as your sideboard similar to draft format, but this is unconfirmed