So this "was' kinda forbidden knowledge, but as a father of 2 months daughter, i don't have time to start new game over and over and over again, after any kind of updates / new fixes of map mods.

Disclaimer #MYENGLISHISNOTVERYGOODLOOKING

Being myself a bit of a modder, but for personal use and i found (red about it, improved) method to add map to existing save or reload any "chunk" of map you wish for your save.

This works for:
- adding new part of map
- reloading after update's
- wiping out chunk of map (so you can AGAIN enter town like never before to loot again / or kill 3000 zombies)

1. You need to start a new game (save) with all mods you have now + with new maps you wish to have - lets call it MAPSAVE
2. Once it loads, exit game, you are done here
3. Go to your save folder (i think for most is C:/USER/Zomboid/Saves/)
(your save is within one of the folder, i always play Sandbox so it is Sandbox for me)
4. BACKUP YOUR SAVE FOLDER - kinda usefull you know.
--------- Now the fun part ----------
5. Copy and overwrite file "map_ver.bin" from that MAPSAVE folder to your save

IF you didn't visit that part of map you are adding YOU ARE DONE, GOOD, FINISHED -> GO PLAY

Warning: That part of map will be removed, cleansed, wiped out, nothing, nada. No bases, no loot, no vehicles and no zombies if you wish
It will LOAD again like you never visited it before.

1. Go to your save folder (you might backup it)
2. Remove map_XXX_YYYY.bin files that are dedicated to that part of map you want to remove
But how do I find which? There are several ways:
- Ask developer
- Spawn in that location and then check what are names in MAPSAVE folder
- Use minimap (there is GPS track at the bottom f.e. 8066-10662 which means it is in map_806_1066.bin file)

for example BLACKWOOD mod those are files:
map_780_1050.bin to map_780_1080.bin (30 files)
map_781_1050.bin to map_781_1080.bin (30 files)
... etc etc
map_810_1050.bin to map_810_1080.bin

Total of 900 files.
3. DELETE THEM. ALL 900. (This will reload building)
4. DELETE chunk file for that part of map: chunkdata_26_35.bin (This will reload loot)
5. DELETE file zpop_26_35.bin (This will remove zombie info, so new spawn)

I know there are some who knew that.
But for others - I hope it will be helpfull.

EPD

My guide works for MP as well. Just create new single player save with maps you want to add, and then take map_ver.bin and replace old one on your server!