Yes, changing which pockets exist in the game is easy (edit the array in Settings, and make sure the couple of other settings there are accurate). The hassle comes when you also need to edit items.txt to move each item into the appropriate pocket, and edit various graphics to suit the new arrangement of pockets.
Off the top of my head, the graphics that need changing are the various Bag ones in Graphics/Pictures, plus the pocket icons in the folder Graphics/Icons with the names bagPocketX.png.