If you reselect which player an attacking creature is attacking, that creature is still considered to have attacked the player as declared, but it is now attacking the new player.

The player Capricopian is attacking can’t reselect it to attack a planeswalker instead. If Capricopian is attacking a planeswalker, no player may activate its last ability.

Reselecting which player a creature is attacking doesn’t cause “whenever this creature attacks” abilities to trigger.

Reselecting which player a creature is attacking ignores all requirements, restrictions, and costs associated with attacking.

The player Capricopian becomes attacking may activate its ability, perhaps sending Capricopian right back towards its original destination.