Yes! That is the way I use it. I have stellaris since release and own quiet a few dlcs, but they keep pumping out more and more so I went the high sea route about a year ago. It makes it even easier when you have the base game legit on steam, because then you get access to the workshop and dont have to work around it when you want to play modded.
Most uploaders there post the dlc files separate from the main game. You can just pull them in Stellaris' DLC folder and overwrite all (I own some of them, but still do it). Then follow the instructions for CreamAPI (I'm on linux, so I use this) and launch Stellaris. The launcher will complain that it cannot verify ownership for the DLCs you dont own, but I had no issues playing singleplayer and multiplayer, both as host and client, with this method.
Downside is that you sometimes have to wait with patches to the game until new files are uploaded on the forum.
(The same method also works for Hearts of Iron IV and other Paradox titles)
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