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 IDEALMAP
2. Once it loads, exit game, you are done here
3. Go to your save folder (i think for most is C:\Users\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 IDEALMAP folder to your save

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

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IF you ALREADY visited that part of map use the B42ChunkCleaner[buchojefe.github.io] and delete the zones where the NEW map or maps should be.
Warning: That part of map will be removed, cleansed, wiped out, nothing, nada.