I don't know the topic but it's pretty easy using the -UserDataFolder launch option. Here is my desktop link for Darkness Falls, using a21.2 and loading mods from and saving to d:\7d2d\UserDataFolder\DF21 (I just used "userdatafolder" for the folder name to keep it clear, can be anything).
D:\7D2D\a21.2\7DaysToDie.exe -UserDataFolder=D:\7D2D\UserDataFolder\DF21 -logfile D:\7D2D\UserDataFolder\DF21\output_log.txt -usenativeinput -skipintro
On the D drive (edit: not smiley face) i have a 7D2D folder and in that folders for each version of the game I currently have installed. I also have a UserDataFolder where all the saves and most mods go.
-7D2D
--a20.7UL
--a21.1
--a21.2
--a22
etc.
and then
--UserDataFolder
---vanilla
---DF21
---Prepocalypse
etc.
This won't work for all mods, like Undead Legacy has to be installed in the game folder, so that will get it's own copy of the game, e.g. a207UL in the above example.