If you wanted them on another computer, couldnt you just copy the .zip file in the dlc folder, and treat it like a normal mod installing it on another?
I am less enthusiastic about this feature, because so far there are two major problems:
1) Password is shown when typed, it should be masked as usual
2) The DLCs are shown as installed and the only option you have is "Reinstall". This is wrong, however - after logging in, those DLCs are NOT installed, you have to click Reinstall, quit the game, and only then they are available in the Paradox launcher in the DLC list.
You cannot back up DLC content and just copy it to another computer without internet access.
However, you can install the game and DLC, start the game once after all DLC has been installed, and _then_ disconnect that computer. The DLC will then have been verified for that computer and you can play the game in offline mode.
Very nice stuff, dear Paradox ! I love those DLCs