Now, Erebor will have as strat map banner the Arkenstone. This is a minimid strictly edited for Divide and Conquer V4.
Go inside your Third Age folder, paste the compressed file and unzip it, yes to overwrite all the files, play, enjoy.
PS: If you don't get the warning for overwriting the files, you're not correctly installing it.
PS2: I don't know if this would be compatible with old versions from Dac, Third Age Reforged or Third Age vanilla, feel free to test it. But first at all, make a backup copy. Compatible with saved games, DacV3 and DacV4.