Changing the back glass is dead easy and takes a maximum of 5 minutes:
- remove the 2 pentalobe screws
- slide the glass out
- put the new glass in
- screw your screws (or replacement phillips screws) back
done!
I am not sure is this voids the warranty, but it should not...
changing the front glass is a bit more engaged, and involves removing the back glass, removing the camera, the microphone and other stuff then remove the whole mother board and stuff
Btw, this WILL void the warranty as there are tappered screws inside (the ones that fix the antenna framework to the front panel, from memory, I watched a video to change the button... never got to change it, as I found a way to soft-reset the button sensitivity).
So this operation is both more involved, more prone to errors and accidents and voids the warranty... no wonder it is more expensive than the back to change...
without counting the fact that the front panel is an active screen, while the back is... static... ;-)