Add an application to the Open With Menu
Well this is defined per app in its manifest. It registers to a certain Intent.
The app that implemented the 'open with' option checks which applications react to a certain Intent, and shows the list of those applications.

I don't think you can modify this at runtime.

(Or you could create a new application which reacts the the 'open with' and creates another Intent which the photo editing app reacts to.)