Allows map makers to force a template world to be chosen from instead of a creating a new world. This is designed for modpacks with worlds that are premade.
As a user to make a new instance click the "Create from template" button on the world list and select the world you want and then give it a name!
As a mod pack dev:
In the game directory, you will want to put the map in the "maps/" folder. Inside this folder you want create a info.json file with the following contents
{
"author": "No Author",
"thumbnail": "icon.png",
"description": "",
"sort": 0
}
This is based of Hardcore Map Reset by Modmuss50