/name <value> allows you to change your name from the console.
"/dumpuser <playername>", when used on a bot, you can see that a skill level 1 ("I can win") bot has handicap 50, a level 2 ("Bring it on") bot has handicap 70, a level 3 ("Hurt me plenty") bot has handicap 90, and level 4 ("Hardcore") and level 5 ("Nightmare!") bots have no handicap.
/handicap <numeric value between 1 and 100> is the console command equivalence to the Handicap setting. Since the "player settings" menu allows for changes by 5 units, if you use the command console to set your handicap, for example, to 91, and then you go to the "player settings" menu, your handicap will be rounded (in this example, to 90).
/color1 <value> and /color2 <value> store inner and outer colors respectively. The default values are 4 and 5. These variables use values from 1 to 7 for the available colors (1 = dark blue, 2 = green, 3 = azure, 4 = red, 5 = violet, 6 = yellow, 7 = white).
/cg_oldrail 1 affects only the main beam: this will affect all railgun shots you will see (fired by you or by other players), but will not affect other players' screens. More notes in the Development trivia section.
/model "model name/skin name" is the game's equivalent to the Model section. It affects non-team-based modes.
/headmodel "model name/skin name" can be used to mix a model's body with the head of another. Using different characters for body and head may produce weird/funny effects; again, you can omit skin name. It affects non-team-based modes. Just select a "model" again to have the head return normal.
/team_model and /team_headmodel are the equivalents of model and headmodel for team games. In team modes, red and blue "skins" are automatically used, so you do not need typing "/red" and "/blue". You can still specify a skin name though: while some skins just use the main model's red and blue skins, others do have their own red and blue color variations (even if they are not shown in model selection screen).
/cg_forcemodel 1 (default value is 0). During non-team-based gametypes, you will see all player models look like yours. During team-based gametypes, instead, you will see all the players look like the Sarge character.
In OpenArena 0.8.5, black text appears as white, while used in player's names (this to prevent people from trying to avoid recognition by using black text -hard to spot in front of dark backgrounds-); in OpenArena 0.8.8, black text is shown as black again, but only if the name contains at least a letter of a different color.
Older versions of Quake 3 Arena featured only a railgun trace with a simple colored ray with "dots" placed at fixed distance along the beam, inside it (and of the same color), without the outer spiral (at the time, railgun trace color was controlled by a single variable, called simply /color), but the spiral was a cool element gamers had seen in the previous Quake II game, so id Software later added the outer spiral of dots with a PointRelease, introducing the cg_oldrail variable for those who did not want the spiral instead, and removed the old "inner dots" effect for both modes. Those "dots" can still be seen while playing with a small number of old mods that maintained the first railgun trace style (with dots inside the beam, of the same color), as Rocket VS Rail.</ref> It's more a "graphic option" than a "player setting", but we mention this here so you know that it would seem that nothing happens if you change the second color when you have /cg_oldrail 1, while it may actually change the color other players would see your railgun spirals.
The new name will be used in the current mod; remember that, when you first run a new mod, your name and many more options are copied from the configuration of your baseoa\q3config.cfg file, and successively configurations are independent for each mod, this meaning that if you later change your name, you will need to manually change it for each mod (unless using some external tool that allows to maintain the configurations aligned).
It is even possible to manually edit your q3config.cfg file with a text editor and change your name there, or to use an external tool, like Quake 3 Name Changer or, better, OpenArena Name Changer (these tools allow to select some symbols and to select if to apply the new name only to one, to some or to all mods).
To quickly change your nickname, e.g. adding and removing your clan tag as needed without re-typing the name each time, you may bind two different "set name <nickname>" commands to two different keys (see command console), or place them in two different configuration files (that can also be one-line long and that you would then launch using the "exec <configfile>" command), or use the "favorites" feature of the OpenArena Name Changer external tool.
Usually you should leave the Handicap setting to "none", but if you are a "pro" (very skilled) player and you enter a server with many "noobs" (new/unskilled/casual players), and you kill everyone too easily (for example, you win a FFA match with 50 frags, when the second player ends with 20 frags only, the third player with 10, etc.), please consider the option to set an handicap for yourself, or to search another server with more experienced opponents: for other players, being "owned" (totally surclassed, dominated) is frustrating.
Some mods allow to customize the default character for team-based gametypes, or even to set a specific model and color only for enemy players. This won't be part of the main game, ever. "Force player models" option was initially designed to save memory usage.
Models are in MD3 format. If you choose a non-standard model, you will see it when playing locally, but when connecting to another server (with "sv_pure" option enabled, as usual), it will be temporarily replaced with the default one, unless the server has got the same model installed. Additional skins desigend around Q3 characters may not be shown if there isn't a model with the right name in OpenArena; and if a model with the right name exists, the skin may appear more or less "messed up", because the OpenArena 3D model is not exactly like the original. However, you can try it and decide if you like the result or not. To avoid such things, you should download "complete" models, usually those you find in pk3 files bigger than 1 MB, instead of simply additional skins for Q3 characters.