go into your library
click on RTCW
click Add Command Line Parameters
in the blank, enter +set sv_cheats 1
this will enable cheats
This isn't working with the new "GOG Galaxy" app. There's nowhere to add command line parameters
right click on the game icon, select Manage Installation > Configure
put a check in "custom executables/arguments"
Click "duplicate" under file 1 executable
drop this is the argument field for file 2 executable "+set sv_cheats 1"
make file 2 the default
apply and save and then run the game