The following CONSOLE VARIABLES are made available (replace the # sign with a number), in-game help is available by typing the "LISTVAR" command at the console:

"MOTIONTRACKERVOLUME" - this is set at its maximum of 1.0 by default, the volume of the tracker can be reduced by changing this number (e.g. to 0.75 or0.5).
"CROUCHMODE" - this new console command allows players to change the Aliens crouch/crawl to a toggle on/off key by typing "CROUCHMODE 1" at the console. "CROUCHMODE 0" changes back to the default setting.