For you to be able to edit a mod or to make a patch for it, you need a copy of it in the
..\Steam\steamapps\common\Kenshi\mods folder, and the mod folder's name needs to be changed to the exact same name as the .mod file inside it.
First copy the number part you see on the mod's (you want to edit) steam page's link (open kenshi workshop and the mod page) like steamcommunity .com/sharedfiles/filedetails/?id=2319337000 so copy the number part '2319337000' (whatever it is for your mod in question)File:Copythenumberpart.png
Go to file explorer in your computer and navigate to the Kenshi installation folder. Go back to steamapps folder and click open the ..\Steam\steamapps\workshop\content\233860 folder.
use search within the 233860 folder with the number you copied. You'll find the original mod. Allow it to load entirely. Copy the folder. File:FindFolder.png
Go back to Kenshi/mods and paste the copied numbered folder there.File:PasteInMods.png
Go back to kenshi/mods and rename the numbered folder with the copied mod name. Or alternatively rename the mod file and the folder something else. If you used the original mod name, unsub from the original mod. Mod folder needs to be exactly the same name as .mod file, otherwise FCS won't recognize it.
Now you can open the copy mod in FCS and edit it to your heart's content.