You cannot play multiplayer, and you must re-authenticate online every 30 days.
Assuming you find a working CreamAPI configuration for Warhammer 3 5.0, here is what you risk. dlc unlocker total war warhammer 3 portable
In recent years, the demand for portable DLC unlockers has grown significantly. A portable DLC unlocker is a self-contained software package that can be run from a USB drive or other portable storage device, allowing players to unlock DLC content on any computer without the need for installation. You cannot play multiplayer, and you must re-authenticate
A portable DLC unlocker means you can take your unlocked game with you, whether you're playing on a friend's computer or traveling. There's no need to worry about installation or compatibility issues. A portable DLC unlocker is a self-contained software
While bans for using API unlockers are rare in the Total War community, modifying steam_api.dll technically violates Steam's Terms of Service and could result in account-level actions if Valve's DRM detection evolves.