With gtk-can-change-accels = 1 set in ~/.gtkrc-2.0 you can change an application's keyboard shortcuts by hovering over the menu item and pressing the new binding. Comix assigns the new keybinding, and will read it correctly, but on opening the program again it does not remember the assigned keybind.s I tested this in other GTK apps which do save the custom bindings on closing.
1. Add the line "gtk-can-change-accels = 1" to ~/.gtkrc-2.0
2. Open Comix
3. Click "Edit" menu, hover cursor over "Preferences", press C-p
4. Click out of menu, press C-p, Preferences window opens.
5. Exit Comix, re-open.
6. Press C-p, accelerator no longer works.