Quote Originally Posted by Cooper View Post
The core changes of the DLCs get patched into the main game for all owners of CK2. So things like the Old Gods pillaging and pagan kingdoms will exist in-game for all players, even if they do not own the Old Gods DLC. What buying the DLC allows you to do is actually play as those added components (trading empires, pagan kingdoms, Islamic kingdoms etc.)
Did they change stuff?

It was at least on release of Old Gods time that as long as Host has a DLC enabled, everyone can use every aspect as if they owned the DLC as well. I've played with Ruler Designer and played old gods before i bought it myself, just becauser friend hosted game with those up.