Is it possible to create a script or shortcut for the UV-editor "save as image" in 3d view instead of while you are in the 3d editor?
The Save as Image operator is only available while the UV/Image editor is active, it will save the visible image to disk. Once the image has been saved to disk you can use the Save all Images while you are texture painting in the 3D editor to save all changed images to disk. The toolbar already has a button to do this while texture painting.
If you want to use a keyboard shortcut you can create a new entry in the input preferences, under 3DView either in Global or Image paint would work, then fill in
image.save_dirty for the operator and choose the key combination to use.
You can then save user settings and have it available every time you run blender.