Pretty sure he means whenever the map is changing, the specific script will be changed too. You can just rename your map.lua file to the name of the map and put it in the maps folder. In another way, you can do with this simple code (that code it's not really mine though).
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if ((string.len(map("name") > 2) and (string.substr(map("name"), 2) == "zp")) then
dofile("ZombiePlague.lua")
else
dofile("Default.lua")
end