I'd like to install some purely aesthetic mods like the custom skyboxes. Will this flag me as playing a modded version in terms of multiplayer, same as if I'd installed a balance changing mod? If not, then how does the game separate between the two? Could I be playing online against someone decked up with UI mods that give him an advantage, without knowing it?
The game consists of 2 parts: The Client: This is the program that displays the world of the game to the player, as well as draws the UI and lets the player interact with it. Apart from giving commands to units it has no further control over the game. Clients are also never given more information than they need to know. So maphacks are i.e. impossible. The Server: This is the program that simulates the game. No matter how many players are in a game there is only one server. This is usually hosted somewhere in the cloud. The server dictates what units a player has, where they are, what stats they have, etc. It tells the clients what they need to know and accepts (or discards if they try to cheat) commands from the clients. There exist 2 typs of mods that match with this: Clientmods: These modify the client. They change the looks of stuff, they can change the UI, they can offer an "easier" UI to a player. But they do not affect gameplay directly. The usage of client mods is invisible to the server and thus also invisible to other players. This means you could play vs somebody with mods that massively change how the game looks, but they will be playing the same game as you are. No changes to gameplay-relevant stats are possible. Nevertheless ofc a good UI is an advantage, so I'd consider looking for UI mods that you like as part of what a good player should do to be a good player. Servermods: These can change stuff on the server side. This means gameplay. They may rebalance stuff, add new units, change winning conditions and do other drastic stuff we are not yet aware of. A server mod is activated by the host of a game and is active for all players. You can see that a server mod is active in the bottom left of the lobby. Active server mods show a textbox there. So: Yes you can replace stuff like skybox textures without anybody realizing you have. You can also change the UI without anybody realizing, giving you a little advantage. You can't however do anything more powerful like maphacks, or economy cheats without a server mod.
