You can't modify the default menu. You can disable the menu and create your own. You can make it look similar using the new Card Windows feature in FM16.
Set the container as non-editable in the inspector. This will disable the buttons since you can't trigger them by clicking in the field.
Use a button for replacing the contents of the container field. You can create a regular button on the layout or convert the container field into a button. Use the proper FileMaker function to replace the image.