Originally Posted by 13chillz

Idk what sai can do.

Photoshop and gimp have an offset filter which allows you to work on the back. Or you could merge all the layers and fix the back at the very end. Or you could expand you canvas and copy your layers so you have basically two heads side by side which would allow you to work on the back then copy it back to the original. A long time ago I used to make a merged copy of all my layers and then do what calamity said. Then when you put it back you erase everything but the back so it's sort of like a patch.

There are multiple ways to skin a cat. You just have to find out what your program will let you do. Personally I just use a offset script that offsets all my visible layers in PS that I found online somewhere so I don't have to merge layers.