Happy Hour:
I think it would be good fun to have 1 hour everyday in which anybody can teamkill/map glitch all they like because everybody knows it's a whole lot of fun, but only for this one hour. This way people can get it out of their system and it adds a new dynamic to the server spicing things up a little. (this does not mean client side cheats/hacks are allowed)
Rule exceptions:
Have you ever played ZE when there has been 5 or less people on? Then you know it's pretty dull. I think when there is less than 5 people online, the early nuke/teamkill/glitch rules should be put aside because it makes things more interesting and fun. It also means mas such as boatescape can be finished in good time when 1 of the CT's decides to camp at spawn and can easily fend off the few zombies online, so the CT ahead can early nuke that dude.
To allow happy hour you could have an automatic message appear at the allotted time to signal to players when it's happening. Maybe change everyone's text colour to a certain colour so any SS or demos people upload will clearly show when happy hour is taking place so there is no confusion with enforcing normal rules.