I'm not sure what NPC rules state. However, IFBB rules say you must have the hair off the shoulders in pre-judging. I think you should try to make the best impression at pre-judging because you are amongst a bigger group of girls and you need to make a big impact. I have always put the same effort in prejudging hair/makeup as I have with finals. You worked your butt off. Don't give the judges a reason to overlook you.