Thank you.
If you are using the old-school cd-version like me, then you just have to create another folder and rename it into something of your choice such as TLK_Original. Then whenever you wanna play it you rename it again to "Last_Kingdom" and rename my submod to something of your choice such as "TLK_WotN".
Edit: The one you wanna play should always be named "Last_Kingdom" - the other one should be temporarily named to something else. Start by installing TLK 3.06 and then add my submod as a separate folder - they cannot be named the same thing at the same time.
As for Steam i am not sure.