There should be some pretty good modding tutorials on youtube but the way i would go about it is find out if the zombies sight value is a number and set it to 0 or if its string find a way around it, i have no experince with LUA but it doesnt sound too hard, or there is the mod where it makes you blind, with the modders permission you could probably use some code from that to see how he does it.
Edit: http://www.lua.org/pil/contents.html this is the manual for LUA, Have fun.