Windshaper Planetar

• WOTC Official Reminder Textofficial rules
  Flash — You may cast this spell any time you could cast an instant.

• WWizards of the Coast2022-06-10
  Official Ruling
  Reselecting which player or planeswalker a creature is attacking ignores all requirements, restrictions, and costs associated with attacking.
• WWizards of the Coast2022-06-10
  Official Ruling
  If you reselect which player or planeswalker an attacking creature is attacking, that creature is still considered to have attacked the player or planeswalker as declared, but it is now attacking the new player or planeswalker.
• WWizards of the Coast2022-06-10
  Official Ruling
  You may cast Windshaper Planetar outside of a declare attackers step. If Windshaper Planetar enters the battlefield outside of a declare attackers step, its ability simply doesn't trigger.
• WWizards of the Coast2022-06-10
  Official Ruling
  Reselecting which player or planeswalker a creature is attacking doesn't cause “whenever this creature attacks” abilities to trigger.
• WWizards of the Coast2022-06-10
  Official Ruling
  If an ability targets something controlled by the “defending player” of an attacking creature and the defending player for that creature changes before that ability resolves, the ability won't resolve because its target has become illegal.

Rulings via Scryfall