How do I change the character of the third and fourth cpu?

[fmohiy]

Often times, I'll want to change the third or fourth cpu to a workshop character, but none of the controls I've tried work! can someone help?

[Teal Phoenix]

Click the arrow swap button when there's no player in that slot to switch your controller to that slot. Choose a workshop character like you would normally, and then click the arrow swap button on your original slot to switch back.
Now when you set the player 3 or 4 slot to a cpu the character from earlier will already be chosen.