The new X4 DLCs go right on the list...
"To access your bonus content through GOG, please register your game on our forum:
1. Visit
https://www.gog.com/account and click on X4. Navigate to "more" and "Serial Keys" to find the serial key you will need to register your purchase.
2. Visit
https://forum.egosoft.com/ucp.php?i=-egosoft-settings-ucp-gamereg_module&mode=gamereg and enter the serial key you found on GOG.com into the "Game Registration Code" field at the bottom. Click "Submit" to register your game.
3. After registration, your Yasur light fighter ship will be waiting for you in the in-game Venture Inventory once the Multiverse Team Seasons start. The other bonus content will be downloadable from the "Extras" section of your copy of X4 in GOG Galaxy or gog.com.
To access your Yasur, your save game must first be converted to an online save game. Playing online "Ventures" requires you to opt in to the "Multiverse Team Seasons" public beta, which will launch at a later date. You will also need to register an Egosoft account, connect your game to your Egosoft account in your User Control Panel and log in in-game using this account.
To access your exclusive Pearl Prospect paintmod (10 copies per savegame), you will need to register an Egosoft account, connect your game to your Egosoft account in your User Control Panel and log in in-game using this account."