The answer to the question of whether online games can be modified is a bit more complicated than a simple yes or no. While it is true that you have the right to modify a single-player game, the same cannot be said for online games. There are a number of multiplayer games that allow for modifications, such as Team Fortress 2, Ark, Rust, and many others. However, it is difficult to predict how developers and publishers will react to modifications made to online games, so there is always the risk of being banned from using mods in a multiplayer environment.
It is important to be aware that any mod used should not be considered a cheat. Mods can be incredibly beneficial as they use the same development tools as game developers. This means that even older games can be given new life with the help of mods. For example, The Elder Scrolls Online exists, but playing Oblivion and Skyrim with friends or strangers can still be an enjoyable experience. Additionally, mods can be posted online for others to use and get feedback from players on what they think.
Modding is an incredibly popular activity that involves modifying someone's game to create new content within that gaming world. Although there are bugs and flaws, it is still an achievement that even a twentieth-century single-player game can receive a working multiplayer mod. For example, The WWE Games has been known for the modding that takes place, especially since the game's own content sharing service allows it to be disseminated. The ability to compromise a game depends largely on what is sent to the client's games and the amount of verification that is done based on player input. Finally, some very skilled and lucky modders have created their own game based on the concept they created during modding.
While you no longer need a mod to play multiplayer in this game, the original mod was so influential that it deserves recognition. The Nexus Mods site (opens in a new tab) houses simple and complex mods for more than 600 games, mostly role-playing games from Bethesda such as Skyrim, Oblivion and the Fallout series.