STOP RIGHT THERE!
(First of all, this thread was the one you were looking for, everything related to modding is placed in the workshop section ;p)
Now, don't get confused, adding new DLCs is actually easier.*
You just need a DLC and the model you want to use.
You can read how to do it here. It also has the files you will need ;9
*You can use that info to replace the official DLCs if you want to, but there's no need to do that.