Choosing friend or foe for each player is done while Khorvath's Fury resolves, not while it's cast (C.R. 608.2d, review C.R. 601.2). Thus, such a decision isn't copied when Khorvath's Fury is copied and a different choice can be made for the copy than for the original (C.R. 706.10, 608.2d).
EDIT (after comment 4 was posted): See also this thread.
EDIT: Edited last sentence after comment 4 was posted.
EDIT (Dec. 31): Deleted a clause.
1) The choice is made upon resolution. It is part of the spell's effect.
2) When you copy the spell, no friend/foe choice has been made yet. You choose for the copy when it resolves, and independently of that choice, you choose for the original when it resolves some time after the copy.
Question 1: When do I choose the "friend or foe" part, when I cast the spell or when the spell resolves?
Question 2: When I copy Khorvath's Fury, can I choose the "friend or foe" part anew or must I pick the same modes of the original spell?
EDIT (after comment 4 was posted): See also this thread.
EDIT: Edited last sentence after comment 4 was posted.
EDIT (Dec. 31): Deleted a clause.
2) When you copy the spell, no friend/foe choice has been made yet. You choose for the copy when it resolves, and independently of that choice, you choose for the original when it resolves some time after the copy.
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