You can't really change the things camera intent has to offer, and if you do find a device where the camera app would let you access the gallery I wouldn't depend on it.
I am a user of the BuitenBeter app. With this app Dutch civilians can easily report issues to their municipality by taking pictures. The app offers me only the possibility to upload pictures from the camera and not from the gallery. I spend several hours looking for an app which I would name
Camera2Gallery, which would appear as a extra option in the screenshot below.
Does it exist? Can it be easily made? I think there is a real big need.