If you want to edit keyboard shortcuts, you need first to change /org/cinnamon/desktop/interface/can-change-accels. You can do that with this code in terminal:

$ gsettings set org.cinnamon.desktop.interface can-change-accels true

Edit or create ~/.gnome2/accels/nemo and add the following line (replacing "F4" with the desired key combination):

(gtk_accel_path "<Actions>/DirViewActions/OpenInTerminal" "F4")

<Alt>, <Primary>, and <Shift> can be used as key modifiers (for example, <Primary><Shift>t).