OK, I got it to appear. This file lowers the bridges too, but keeps the zombies.
Thanks to Colonel Stan for verifying that original versions didn't work, lol
If you want to edit the file, open the sr3_city.lua file with Notepad++ and scroll down to function sr3_city_main(). -- is for commenting out lines. Comment/uncomment stuff as you'd like.
Of course, Sandbox+ would be a better way to achieve this, but more options is nice for people that don't need the hassle of installing it or want the extra features.