Didn't even think about it until I played a shorty round with chamber running around with a deagle. It's the only side mode from normal games that persists so I at least think it's worth looking at to either disable him or come up with som...

I just recently learned this and its actually pretty cool. This is especially helpful when you practice your lineups in custom. Happy learning! Also, if you have any other similar tips during custom games, share your wisdom!