This is the biggest dealbreaker. While low-level server admins might not notice, many popular online leagues (Sim Racing System, World Sim Series, private lobbies with AC Server Manager) run integrity checks. If the server detects that your client claims to own DLC that Steam says you don't, you will receive a "Checksum mismatch" error. Persistent use can lead to a Steam account ban (though rare for AC specifically, it violates Steam's Subscriber Agreement).
If you use Content Manager (the third-party launcher considered essential for any serious AC player), you typically run the unlocker before integrating CM. Some modern unlockers are built directly as Content Manager plugins. dlc unlocker assetto corsa full
: Some websites and forums claim to offer DLC unlockers for Assetto Corsa. However, I strongly advise against using these, as they may: This is the biggest dealbreaker