I would think that rather than opening the default camera app and activating the third party app from there you would just open the third party app itself to take your pictures. I haven't gotten deep enough into modding to change actual button assignments, although I would like to You would have to be rooted to do that so you would have the appropriate rights. While I am rooted and have done some modding, you may get better answers and more feedback in the Rooting and Hacks section. Good luck