Alright so I just patched together a fairly rough thing, basically the thing is, last year I had to trigger all the zombie spawns myself so it required me to be on the server in order for it to happen. This year however I made a way for super admins+, so theoretically (in alphabetical order) Bolli, Fredy, StephenPuffs, Swiper the Fox, Tanges, or Xquality could trigger the event to happen. Who I will instruct on how to do so.
Basically all it is, is you will need to type "spoon" into your console, which will either opt you into or out of the event when it is triggered, as that seems to be the common phrase we use to know who wants to be in one. Then when the event admin wishes to, he may trigger the event to begin, which creates X amount of zombies (classic and fast) around you, and you are given a gun for Y minutes (up to 5) with unlimited ammo. Presently this gun is an AK-47 but that is subject to change. Using this gun to attack other players with that being your clear intention can/will result in a ban. So no saying "YOU'RE A ZOMBIE!" then proceed to shoot that player, unless you enjoy bans going on your record and not being able to participate for the rest of the day. And yes admins can easily monitor this to be sure you aren't.
Rules during the zombie invasion other than the use of the gun which I already mentioned are fairly simple. Do not use a vehicle to run over the zombies no matter what, only use firearms (or if you feel daring, a knife). Weapon laws should not be enforced by police during the time with zombies unless they catch someone killing another person purposely with their appointed weapon, that action would still be considered murder. Police are allowed to use their weapons to help save the civilians from their zombie attackers, but be sure to use selective fire. Do not abuse the event and use it in a negative manner, it is held to have fun and a time where I don't care how trigger happy you are, as long as it is against the zombies only.
Other basic rules are, you need to be a civilian, not in a vehicle, and be outside when the event is triggered, otherwise no zombies appear thus no gun either.
I'm sure there are other things I'm forgetting, but it's easy to follow if you simply use common sense and participate in good faith.
Like I said, it's nothing way over the top, but I put this together in about an hour or so, so hopefully it should be fun as long as people follow the general guidelines I have put forth.