I'm not sure, but you surely can deactivate it.. but i guess it's done somewhere in the gameplay constants or at least in the player config, so I don't know if it's possible to turn it off or on like you said..
But what about creating your own tradesystem? like the one from Burbenog TD.. like "-give 20 02" which will give 20 gold to player 2.. you can make these commands seprate and only enable the ones you like.. and give an info or anything like this "tradesystem activated".. i like this idea more, than changing the normal F11 function