Press CTRL and ALT and ~ ( Above the TAB key ) to bring up the command console in a single player game.

Change the angle your character is viewed in thirdperson. 180 is a front view - pm_thirdPersonAngle [Value]
Change the distance the camera is from you in third person. 0 is a face view, 80 is default - pm_thirdPersonRange [Value]
Change the height you are viewed in third person. Negative numbers are below normal - pm_thirdPersonHeight [Value]
Play from third person with your HUD, crosshair - pm_thirdpersondeath 1