It should be valid to redeem (for antagonist tokens) any sort of antagonist (custom or round-ending) during an extended round with a 'first come, first serve' basis (so as to not overcrowd the server with antagonists; nor overwhelm the crew; nor create too many different factions of antagonists; etc).

Certain time limitations could apply to make it so players have some time to play the round on 'Extended' game mode before it's customized.