almost 2 years ago - Shurenai - Direct link
Iirc backing up a save and just renaming the duplicate should do the same thing you're after.

Saves are located in:
C:\Users\\AppData\Roaming\7DaysToDie\Saves\\

Copy the right save, and just paste it into the same location to create " - Copy" an then rename that copy whatever you want.

Or you can copy it to a new location, rename it, and put it in the original location- Whatever the case, Just make sure you're putting the copy in the same world that it's associated with, ie, the same location you're copying from.