Can you sideboard into a different Chosen Champion if you have the unit in your main deck?

Ruling: You can sideboard into a different Chosen Champion, either from cards sideboarded in or even from the main deck during sideboarding. However, you cannot sideboard into a different Legend or include different Legends in your sideboard.

Nuances:

• Your Legend (the card with a domain identity and an ability) can never be changed
• Your Chosen Champion is a Unity with Champion that has the same tag as your Legend
• The terms "Legend" and "Chosen Champion" refer to different card types with different sideboarding rules