Obviously Apple will use some sort of specialized tool for removing the glass, probably some sort of suction cup combined with a frame to grip the metal rim--not too different from a watchmaker's tool for inserting and removing the crystal face of the watch.

As your own photos show, it's going to be almost impossible to open one of these to replace the batteries (or whatever) without leaving a mark. If you're a technician, I strongly recommend getting the right tools for the job; I've seen too many 'hack jobs' done by amateurs running repair shops. I'm not saying any readers here are amateurs, but I'm sure everyone here knows of someone like that.