Too many people have the definition of a "mod" spread out way too much. A mod is a modification to the gameplay itself, not simply any change made to the game, like a new level or player model or skins.
Day of Defeat, Team Fortress Classic, Counterstrike, these are all mods of Half-Life because they change the gameplay completely. A new player model for the singleplayer game isn't a mod, it's just a new player model. If somebody were to make a *shudder*JK2 version of Counterstrike*shudder*, then that would be a mod and would show up in the mod menu.