@deusimperator I apologize if I wasn't too clear, I'll provide a visual guide.
Begin with going to your FAF folder. If you are lost, open the FAF client, click on the 'hamburger' button (I put a 1 there for clarity), then click on 'Show data folder'.
This will open explorer and highlight the FAF folder-open it.
Proceed to the bin folder.
Right click on the faf exe, then click on create shortcut.
This will now create a shortcut to FAF to play offline-you can move this anywhere you want (for example on the desktop). Either way, if you now want to play the coop maps offline, you'll need to edit this shortcut, so right click on it and select Properties.
Add /init init_coop.lua to the end of the target like so:
That's it! You can now play downloaded coop maps by opening the game from this shortcut and going into skirmish, where you'll be able to choose the map, faction, options, and whatever else you want.
As an aside, while you do start these maps from skirmish, you actually load the saves from campaign-it's a bit weird but not too much of a problem at the end of the day.